Catalystik is right. But, to further elaborate:
If you matriculate at the same school you did your SMP at then you usually don't have to retake the M1 courses you already took. For example, at Georgetown during the SMP you take most of the M1 basic science courses (roughly 3/4) plus a few grad courses. If you're accepted, you enter as a M1 (you still have to do a full 4yrs of med school). At this point you take the (roughly 1/4) M1 courses you haven't done plus the doctoring classes. This leaves a ton of free time during M1 you can use to do research, TA classes (anatomy), or get more clinical experience, etc...