Alright, here it goes...
Body lifts just lift the body, hence the name. The ground clearance can only be improved a little bit if you put bigger tires on.

Suspension lifts raise the body and frame together as one which allows for more travel. Since the tires stay on the ground but the body and frame go up, the tires can now travel farther upward before they max out. And since the frame and body are both raised by the lift you get the full amount of ground clearance as the lift (i.e. 3" lift = 3" of ground clearance). The only thing that doesn't get more ground clearance from the lift is the axle between the rear tires. Everything else.. the tranny, front diff, t-case, gas tank, etc.. does get the full improved ground clearance.