Manual mode is just another tool in the toolbox. I use M + Auto ISO ( + exp comp) much of the time (this is technically an autoexposure mode since the camera uses the ISO to maintain image brightness). However, there are times I use full manual too. It depends on the circumstance. As long as you understand how your meter actually works (which in my experience really only applies to less than half of the manual mode shooters out there - sorry), you can use this rule of thumb much of the time:

For scenes with varying light levels but constant tonality, an autoexposure mode is often best (even if you have to use it with exposure comp). For scenes with constant light but varying tonalities, then full manual mode is best.

And if that rule doesn't make sense, then you may be one of the people I mentioned who really don't understand the meter works

My thoughts on using manual exposure:

If all you are ever doing is dialing in an aperture/shutter combination to match "0" on the exposure meter scale in manual mode, you may as well use one of the priority modes instead, as it will not only yield the exact same results, but will also be faster to execute. Faster equals more efficient, and possibly fewer shots missed too.

However, if the situation calls for frequent exposure compensation adjustments, shooting in manual mode can indeed be the more efficient approach, especially if your camera does not have a designated exposure compensation control button/dial that can be easily accessed while shooting in priority mode.

I wouldn't use it unless I know exactly what it's supposed to do. I often use the 24-85mm lens and set my aperture at f/8.0. Minimum ISO 100 and maximum ISO 12,800. I normally shoot object not moving too fast so motion isn't much of a problem.
1. Under the brightest condition I likely to encounter which is "Sunny 16" or LV 14.7 the camera would use ISO 100 and 1/400 shutter speed.
2 As the light gets dimmer to about LV 12.7 the shutter speed is 1/100.
3. The camera by default observes the 1/focal length rule so if I set the zoom to 85mm and the light get dimmer it would increase the ISO. With the zoom set to 24mm it would stay at ISO 100 until the shutter speed gets down to 1/25 which is LV 10.7 before starting to increase the ISO.
4. If the light gets any lower then it simply increases the ISO up to ISO 12,800.
5. At 1/100, f/8.0, ISO 12,800 it's LV 5.7 and it's quite dark. If I zoom to 24mm the shutter speed went down to 1/25 and at 1/25, f/8.0 and ISO 12,800 it's EV 3.7 and the scene will look brighter in the pictures than in real life.

Now that Chaostrain's poll has been out there a few days, and we have learned that "about" 8-out-of-every-10 Hogs set their camera exposure controls manually, I'm just curious (as Chaostrain was originally) as to "why?" The vast majority of Hogs seem to have/use modern cameras that come with a whole lot more Bells-and-Whistles than my trusty Nikon FM did. It sure seems like the vast majority do "some amount" of computer post-processing on their images, so we must admit that they have no fear/distrust of technology. If they/we follow the recommendation of the on-board light meter in setting the camera's controls, then why restrict ourselves to the "stepped" shutter speeds available in our cameras rather than setting the aperture and letting the camera set "what should be" a more accurate stepless shutter speed to get as close as possible to "optimal exposure?"

Digital photography isn't like shooting "unforgiving chromes" was. But every book/article that I have read on the subject still recommends that we get the digital exposure as close as possible to our optimum. And, granted, tweeking expose of images in PP is one of the easiest things one can do in photography today. So I'm sure that there must be a logical reason to shoot "Full Manual." I just was wondering if someone could articulate for me what that/those reason/s might be as opposed to using Aperture Priority where we still set everything ourselves except the proper "stepless" shutter speed that we cannot manually set.