Yes that’s true. However I think recording full game play on high speed video could be useful as well because then you can jump straight to some point and also if you watch the whole thing at normal speed you might notice something and then you can go back and look at it in slow motion and then once you have identified it you can investigate that part or situation with in-game frame stepping and code debugging.
Can't you capture the output of the graphics card directly? Cameras seem like an inefficient way to do things.
Depends on how intensive your game is and how fast your computer is and how much memory you have and so on. Personally I can not afford a top-of-the-line computer.
I meant after processing. The stuff that comes out of the monitor end of the graphics card isn't going to be affected by processor speed or memory, its just raw data being sent to the monitor (unless my understanding is way off).