In this exercise, you're dragging the sled behind you, but you're also pushing against the suspension trainer straps or ropes. The fact that you're holding on to two unstable handles forces the upper body and core muscles to work harder than they would with the stable, upright pole handles of the Prowler-style sled.
Most of us poor slobs have jobs so we don't have the luxury of doing two-a-days, but we figure since it's summer there are a bunch of feckless college students out there doing one bong hit after another who just might be able to take advantage of this program.