There's a definite domino effect in any roping run. Basically, the header has to react to what the steer's doing and the heeler has to react to what the header does. If I rope a steer and duck out of there, my heeler better get to the inside because it's going to be a sharp corner. If I rope a steer and hold my horse in to smooth out and slow down the corner, my heeler better hold his horse's shoulder up and wait until the steer gets around the corner before he releases or he'll end up on top of the steer.
The header sets the tone of the run, and the heeler has to react and do whatever it takes to adapt to the header's moves.
If you get a velvet handle and the heeler cuts the corner too much it can also mess the handle up by making the steer drag or get heavy. It's like reading your option. If you understand how cattle react to certain handles, you can play things into your favor.
There's an old saying that if you don't have a good left hand on you you'll have a hard time becoming a good roper. The left hand basically sets up a run. A run has to be in control, and the left hand's in charge of that. This applies to headers and heelers. It's basically passed on from the header to the heeler.