OK, what I think is that if you don't release them and take the mcat a second time, then both of your scores will show up together. So I really don't see what the point of not releasing them would be, since the schools will eventually see all of your scores (please correct me if I'm wrong)
Now, if you feel like you did bad on test day, you have up until the end of the bio section to void your test. If you do this, no one, including you, wil ever see your scores and you took the test for nothing.
But if you have a panic attack or something during the test, it's a good idea.
I overdosed on caffeine on test day and my vision went blurry during the bio section and I had a migraine...this would have been a good reason to void, although I didn't, for fear of having to retake that HORRIBLE test.