Another reason for implementing the ability to turn off "auto select" is that it allows you to move an object while your mouse cursor is not on top of it. Sometimes the mouse cursor is distracting when you're trying to place an object.
The simple answer to your first questions is: It is always faster to use Hardware OpenGL - the alternative is Apple's Software OpenGL implementation which is awesome - but many times slower than even quite old hardware. That option is simply there for if someone has a video card problem and needs to use software just to get it running...
The checkbox that allows you to specify whether to force the application to only use the integrated GPU is actually setting an Apple property which is valid to set irrespective of any other options - that's why it's a separate option. When any application starts, the OS tries to run it up on the integrated GPU normally (if you've allowed the OS to manage its own GPU switching - which is the system default unless you install something to override this) and then it finds that in our case we want to use OpenGL and it typically decides that best performance will be found on the discrete GPU (if you have one) so it switches to it. What it doesn't know at the time is that we barely need any GPU performance in order to work just fine, so it's a bit overkill. On a desktop computer, that's no problem and is advisable to just leave it alone, but on a laptop that you're intending to use for the day unplugged from the mains, then it makes sense to tick this box, which tells the OS that the application will run just fine on the integrated GPU and then restart - this way, you'll not use the discrete GPU and you'll conserve battery power.
Both of these options are initialised to their defaults (Use hardware OpenGL and Do not force integrated GPU) because these will give best performance at all times and only really need playing with if you have a specific problem.
mattthew got a reaction from morbandit in Auto Select Layer