I did it a lot in college, and it did me a huge disservice in med school. It was relatively easy for me to cram for 2 days and crank out a B+/A-/A on a biochem test because I halfway paid attention in class, but that just made the MCAT harder both because I developed lousy study habits and didn't retain the material for very long after my exams. The crammability of any test is directly correlated with your aptitude, intelligence and baseline knowledge, so do with that what you will.