That was my strategy at first. I figured I'll learn by reading the answer key. But then I realized...
1. Practice tests cost a lot (though... I guess so do review books...). And there are only so many of them.
2. I kept on missing pretty simple questions that were knowledge-based (and only pop up like once in every 10 tests or something), especially in the biology section. As a chemistry major, PS was mediocre for me, but BS was horrible without some reviewing. After just going through the review books, scores went up, definitely.
i.e. I wouldn't recommend it... (I wasted some good practice tests because I started out this way... I should have stopped taking so many when I obviously wasn't ready!)