This is a very common question I see on GMAT forums and one that many of my new students ask me. The misconception is that if you're trying to raise your score on an exam, you should just take that exam over and over and over. The flaw in this reasoning is that it assumes that you will actually get better by mere repetition. On the contrary, repetition merely reinforces whatever habits you have, good or bad. If you want to score higher, you need to deprogram your ineffective habits and reprogram effective ones.
Once you have some basic familiarity with the GMAT (after 1 exam administration) taking many practice exams without putting in considerable study in between (50-100 hours) will only serve to discourage you. Each exam is 4 hours long and grueling. The student at the beginning of this post could have spent 24 hours studying and seen improvements in their scores. Instead they burned a lot of energy and became jaded. Being discouraged will damage your future efforts and make you cynical.
Moreover, not all practice exams are created equally. GMATPrep makes the best ones, and there is only a small finite number. Since the question pool in a practice exam is limited, once you have used a given exam it is useless as a score diagnostic until several months have passed and you have forgotten all the questions.