So I figured something out the other day when I was following. This was kind of an "Aha!" moment, perhaps some of you already understood this... but I figured out why some teachers teach followers to use the Q, Q, S pattern in the turn/grapevine.
The length of the follower's step in the turn changes depending on how far away she is and how much pivot the leader is allowing her. So the closer she is, the less pivot she needs, and the more equal her steps are. But the farther she is, the more she needs to pivot to move around the leader, ESPECIALLY on the backstep. If the leader is rotating in the center at an equal speed, and leading her to follow by opening up his chest rather than leading the distance of each step, then at some point she will feel rushed on her backstep, because she can't step far enough. She has to throw in a quick step to "catch up", and then a small sidestep feels natural right after the quick backstep.
So in open patterns, leading the back, side, front as quick, quick, slow can feel quite natural. Whereas, in close, the timing doesn't matter as much, and S, S, S, can work just as well, sometimes better.
Of course, a good leader can match his momentum with the follower, deliberately slowing down the back step to do it in single time, even in large open steps. All things are possible.