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.
I've titled this article TNT (Tips-n-Tricks) for a very good reason. Many times it's the small things that make the biggest difference. Usually when reading a new book or article you walk away with one good idea. This one idea could've been presented in a paragraph or two. So I got to thinking, why not just provide all those great ideas in a format that cuts out the BS? What you're left with is pure TNT, the stuff great explosions are made of.