Hey, Calicpa! Sorry for not commenting earlier, but as you have already heard most of my thoughts on GMAT preparation, I didn't want my response to further give you a one-sided view of things. But, since nobody has answered your question yet, I guess you're stuck with me for now.
During question practice - not CAT practice - I checked each answer. If I felt confident and answered the question correctly, I would usually just move on. When I was either uncomfortable with a question or answered it incorrectly, I would fully read the explanation at least once, correct my mistake(s), and then move on. I also redid the question usually later that day. During my peak, I could practice with about 40 to 75 questions per day this way.
This was the only method that worked for me. If I completed all of the questions first and then went back to check which ones were incorrect, then I couldn't reinforce or fully appreciate the specific concepts involved for each failed question. Instead of completely going through the problem and the explanation, I just did one-half at a time: one-half on the question, one-half on the answer. There was a disconnect between the two when I practiced this way. Also, I couldn't remember my thought process during that time. It's not just about what you did incorrectly, but how you did it incorrectly.
When I reviewed each question and answer, I was 100 percent focused on that particular problem and knew exactly what was going on in my head. I also felt mentally fresher this way.
For CAT's, however, I never did this. Those are designed more for test practice rather than question practice. Complete those just as you would for the real test. If you feel confident about your answer, then you probably don't want to spend time checking you answer. There's simply not enough time. If you're hesitant, then checking is an option. If you have no idea at all after about 30 seconds, then guessing become a legitimate choice.
But maybe my experience is an unusual one. Perhaps others would care to contribute . . .