Ok I realize that everyone here is a die hard pre-med, so this will probably make absolutely no sense, but:
Consider the possibility that you might not like medical school, might not do well in medical school, or might go through a difficult patch while in medical school. Let's say for any of these reasons you choose to withdraw. Later you decide to reapply to medical school and/or graduate school. Only now the ADCOMs see your undergrad gpa is lower and it looks like you slacked off your last year of college, which is always a negative unless you can justify it.
It's also conceivable that residency programs would want to see your undergrad grades. After all, a lot of medical schools are basically p/f and it is sometimes difficult to ascertain how a student actually performed in classes. Though a do agree that residency programs would probably not ask for your undergrad transcripts.