Personally I've never thought a camera need an aftermarket grip. When using lenses that are big and heavy enough to need help they are provided with a lens mount. What needs the grip is the lens, at least that's been my experience.
I made this inexpensive wooden hand grip. I've seen commercially made plastic supports as well.
Bigger lenses are very hard to hold by the tripod foot. This makes my lenses with a tripod ring easy to hold by hand all day. The camera takes care of itself!
Anyway, it's what works for me!!!
SS

Personally I've never thought a camera need an aftermarket grip. When using lenses that are big and heavy enough to need help they are provided with a lens mount. What needs the grip is the lens, at least that's been my experience.
I made this inexpensive wooden hand grip. I've seen commercially made plastic supports as well.
Bigger lenses are very hard to hold by the tripod foot. This makes my lenses with a tripod ring easy to hold by hand all day. The camera takes care of itself!
Anyway, it's what works for me!!!
SS

Thanks for all the replies. As indicated, I am not looking for any information for myself, but rather to share information and experiences among the group. I agree that the D300 and even higher level cameras in what I've come to call the "medium size" bodies (larger than, say, the D6xx, but smaller than the largest "pro" size bodies sometimes don't feel completely "right" to hold. I've noticed that the bottom corner seems to sometimes hit the meaty part of the heel of my right hand, which can be fatiguing over time. The grip fixes that. It also provides better mechanical advantage when using heavy protruding lenses. To me, the 70-200 zoom when using a grip is no harder to handle than a 24-70 zoom. And the 24-70 handles much more like a short prime lens with the grip installed. That can be important for me, because my 24-70 does not handle VR. I'd estimate that the grip gives me about 2 stops of additional stability, but I've not done any objective experimentation to verify that.

Personally I've never thought a camera need an aftermarket grip. When using lenses that are big and heavy enough to need help they are provided with a lens mount. What needs the grip is the lens, at least that's been my experience.
I made this inexpensive wooden hand grip. I've seen commercially made plastic supports as well.
Bigger lenses are very hard to hold by the tripod foot. This makes my lenses with a tripod ring easy to hold by hand all day. The camera takes care of itself!
Anyway, it's what works for me!!!
SS

Initial disclaimer: This post is pretty long. Some folks don't like long posts, which is understandable. I'm trying to avoid writing long posts, but the "Reader's Digest" version of this one just didn't seem to work, so it won't hurt my feelings if you are one of those and decide that it is not for you and want to move on. It is prompted by my professional experience as an industrial engineer and the ergonomic work that I did as part of a career in that field.

There does not appear to have been much discussion here around the benefits or detriments of accessory grips for cameras, at least recently. I personally have been through a cycle of preference around using or not using add-on grips, but found myself in a situation a week ago in which add-on grips would have been very beneficial. That experience has caused me to reexamine my own preferences. My decisions have already been made and actions taken, so this discussion is not for me, but rather to generate some (hopefully helpful) discussion among the group here.

It may be helpful to know what my history with grips has been. So here goes.

My initial entry to digital photography was with a FujiFilm S5 Pro purchased as a closeout. That camera had a large plastic body (don't remember the exact Nikon equivalent) effectively the same as a medium size body with a grip attached. It was very comfortable to use, and included a second shutter release for use when shooting in portrait orientation. But because it was sooooo slooooow to operate, I moved fairly quickly to a D200, which offered much faster power up, some additional resolution, and faster and less awkward operation. It also chewed through battery charges really fast (or at least it seemed to do so). So I added a Nikon grip in order to have a second battery at the ready and also realized that it made the camera much more comfortable to hold and operate. This was my standard configuration for many years. The D200 grip was different from many current models in that both batteries were in the grip and could be quickly and easily removed for charging. Somewhere along the way, though, I removed the grip and began just carrying a spare battery or two in my pocket. The change was probably made to reduce weight and bulk, but came at a cost. My CBJR flash bracket was designed to properly fit the camera and grip, but would not properly work with the camera body alone...the anti-rotate plate would not fit properly against the bottom front of the camera body.

Later on down the road, I acquired a D300 and D300s, both used. One of them came to me with a couple of 3rd party grips, but neither of them would work properly with either of the bodies. One of them would cause the camera to lock up at random, requiring removal and replacement to reset everything, and the other just didn't work...it didn't deliver all the functionality that it was designed for. And both were of very disappointing materials and build quality. So I never used them. This wasn't really a problem, however, because the D300 went so much further on a charged battery that there was rarely a need even to use the spare that I still carried.

I've written elsewhere here that eventually I needed to acquire a D810 and a specialty lens in order to be able to execute some specialty photography that the D300 was not capable of. Because of cost (which has been discussed here), because the budget was already depleted, and because of my habit of shooting without a grip, I didn't buy one. And when I later bought a D850 to serve as a second body, I again did not buy a grip. Just no perceived need.

So now let's come to earlier this month. I had been requested to photograph our choir's annual Christmas program at church. This was all going to have to be done from the rear balcony, since my worn out knee prevents quickly moving from spot to spot and going up and down stairs quickly. Photographs included "grand" shots of the the entire front of the sanctuary (some including the congregation) at 14-24 mm, intermediate shots of just the choir (70 mm) or ensembles (~200 mm), and tight shots of soloists and trios/quartets (300-500 mm). Lighting was low key, so I was using ISO of 2500 and WB of 2500K in order to provide quick-turn JPEGs in addition to the raw images. This ended up involving 4 lenses on three camera bodies throughout the evening. (14-24 2.8, 17-55 2.8 (on the D300), 70-200 2.8, and 200-500 5.6) Any switching was between the 14-24 and the 70-200.

Both of my hands have some arthritis, and the combination of that, of switching cameras, and of hand-holding the cameras, my hands were pretty tired and sore by the end of the evening. The second night, I decided to try an experiment, so a genuine MB-D10 grip recently purchased on this site went on the D300s and it went back for a second round, even though the plan had been to just use the full frame bodies to capture soloists and small groups. I was astounded to be reminded of how much more comfortable it was to handle the camera with the grip, even though it was a little bit heavier.

The bottom line of all this is that by my calculation, most OEM battery grips are priced at about 12.5% of the price of the cameras they are made to fit. Not really a big impact in light of the additional functionality and comfort that they provide, in my opinion. I wonder whether in at least some cases, addition of a grip should at least be considered as an alternative lower cost and lower impact alternative to a complete system changeout for some of us for whom weight and size seems to have become a problem. I know that is true for me and that I will begin suggesting it as an alternative to taking more drastic measures.

I would be interested to hear about your experiences with these grips.