I was very successful in undergrad as a crammer. I crammed for virtually every exam within 24 hours of the test with the notable exceptions of orgo and physics, which took 2-3 days of cramming each. But that's just not possible in med school. Not only is there vastly more material, but the competition is so much tighter in med school as your classmates have already been sifted through the right end of the bell curve several times over.
Ironically though, I would say that cramming during undergrad has prepared me well for medical school. Compared to many classmates, I'm far more comfortable with the idea of covering a lot of information quickly within a short span of time under high stress. Another huge benefit is that I didn't come in with many bad habits to break (i.e. making notes/outlines, needing to read material more than once). For me the biggest key to transitioning from undergrad to med school was coming up with an independent and cohesive plan on how I wanted to approach each course or module. Setting my own goals and choosing my own resources really helped me become more invested in the longitudinal commitment that's required to succeed here.