The Angry Photographer is not stupid, far from it; and he knows camera gear and lenses. But, he enjoys being judgemental, often negative for effect (Sigma lenses). He is arrogant to a fault, but with some good reason. Like any camera guy, one should watch him for information and knowledge, but take him with a big grain of salt.
He loves to hear himself talk, and spends far too much time repeating himself, re-phrasing what he has previously said; and then saying it again. He will talk for 15 minutes to say what could be said in five.
I will continue to consider his opinions after suffering the through his presentations.

I respectfully disagree. Theoria Apophasis (aka Ken Wheeler) is one of the most knowledgeable and professional photographic bloggers currently publishing. I’m sure others will disagree, especially those whose gear he demeaned. He makes a practice of acquiring lenses he plans to evaluate and does not accept favors or gratuities from manufacturers or major vendors. In short, he is nobody’s “boy” and nobody’s fool. He is aware he has many detractors and, frankly Scarlet, does not give a darn. He calls it like he sees it after detailed in-depth analysis. I respect his opinions despite his rants.

"Always use your lens hood. The lens hood isn’t just good at preventing flare. It can keep you from losing contrast in your images as well as protect your front lens element from snowflakes."

Yes, I'm sure we all have horror stories about expensive lenses destroyed by collisions with snow flakes.

Seriously, though, a lens hood is usually included with the lens, and it's often better than an expensive filter at producing good results and protecting your lens.

FYI, the illustration that Linda from Maine posted is significantly enlarged.

So called "full frame" is the same as the images that most 35mm cameras made: 24x36mm. A U.S. quarter is 25mm in diameter, to help put that into perspective. Part of the reason for "full frame" term being used to describe digital was people moving from film cameras to digital and wanting their lenses to work the same. Today I bet a lot of buyers have never used film... so it's less relevant.

There are pros and cons to both full frame and APS-C formats. (As a side note, I find it interesting that these digital sensor formats both refer to film formats. "Full frame" references 35mm, while APS-C was a fairly short-lived film format, too.)

"Full frame" cameras and the full frame-capable lenses for use on them tend to be bigger, heavier and more expensive. For example, I often use a 300mm f/4 lens to shoot sporting events with an APS-C camera.... that lens cost around $1300 new and weighs about 3 lb., so is easily hand held. In order to use a full frame camera to shoot from the same location and frame my subjects the same way, I'd need a 500mm f/4 lens that weighs closer to 8 lb. and costs almost $10,000... plus a tripod to sit it on, making me less mobile.

"APS-C" format digital cameras are far more widely sold. They use a sensor that's approx. 13x22mm (it varies a bit from brand to brand). APS-C cameras and the "crop sensor" lenses designed for them can be smaller and lighter weight. They also typically cost significantly less. And in most cases an APS-C format camera can use both "crop only" lenses and full frame-capable lenses.

Sensors are made from silicon wafers. Those come in standard "blank" sizes. A typical wafer can make 80 APS-C size sensors.... or 20 full frame size sensors. Plus those wafers sometimes have flaws that cause a sensor to fail quality control. If there are two flaws on a wafer that's used to make APS-C sensors and as a result two of them fail quality control, that's a 2.5% loss. But if the same wafer were used to make full frame sensors, two of which fail, that's a 10% loss. This and the other camera components that need to be scaled up for full frame are the reason that full frame cameras are more expensive than APS-C.

Modern full frame digital is massive overkill for most peoples' real-world uses of their cameras. You don't need a 46MP FF camera to post images to Instagram, Facebook or anywhere else online! Plus APS-C cameras have come a long, long way and seen significant image quality improvements in the most recent generations.

Depth of field and diffraction are actually very little different with full frame, than they are with APS-C. They just seem like it. The reason full frame seem to produce stronger background blur with large apertures actually has little to do with the format... it's how we have to use it, that makes the difference. In order to frame a subject the same way as we were doing with APS-C, with full frame you have to either use a longer focal length lens or move closer to your subject. Or maybe a little of each. These changes are most of the reason that full frame seems to produce stronger background blur effects.

Conversely, full frame also can be used at smaller apertures before diffraction becomes an issue. But the reason this is the case is simply because the full frame image will be considerably less magnified later, to make any given size of print. For example, assuming no cropping is done, an 8x12" print from a full frame image is approx. and 8X magnification. The same size print from an uncropped APS-C image is closer to 13X magnification. So diffraction which is caused by using a really small aperture is going to show up more in the APS-C image, than in the full frame image.

The result of these two factors is that full frame appears to give about 1 stop stronger blur with big lens apertures and it's usable about 1 stop smaller aperture when great depth of field is wanted. This increased range of control with the aperture range can make full frame a bit more desirable for portrait and landscape/architectural photography, for example. FF also may be preferable for macro work.

It is true that full frame cameras can make more noise free images at high ISOs.... but APS-C cameras have steadily improved in this respect, too. There also have been significant improvements in noise reduction software, too. Both formats can make usable images in far lower light conditions and at far higher ISO than was EVER possible with film.

I'd wager that the majority of full frame buyers actually never get any benefit from the larger format. They think they're getting some kind of help making "better images".... but in truth it may be simply making their shortcomings more obvious. And the user is often the only person who actually sees any of the "full frame goodness", while viewing their images "at 100%" on their computer monitors. By the time they've resized the image for its intended use, there's no visible difference that anyone else will ever see.

Full frame also may mean slower continuous shooting speeds and more noise from mirror "slap" and the bigger shutter in the camera. It's also common for full frame to have slower flash sync speeds. And the much larger image files some FF create will also require bigger memory cards, more hard drive storage space and a more powerful computer to work with them.

In the end, full frame never made anyone a better photographer. It's just a tool that can work well when used skillfully for the right reasons. But the exact same thing can be said for APS-C and other digital formats.