The check function takes time which costs you seconds no matter what.
If you achieve your high score by cheating, or not thinking, what was the point of doing the puzzle to begin with. This is like steroids and world records, you bring everything down.
I use the check function when I'm pretty sure that my "logic" was correct, just to double check. Some of the more obscure leaps suddenly pop out at me and I'm not sure why I "know" they're true (those of you more experienced probably find them easy). Anyway, there's nothing more embarrassing that hitting the check button 27 steps later and having half the board removed.