Upon thinking about who likes foot retention and who doesn't, I think one key difference is how well once balances on a bike. I can't do a track stand, but I can nearly do it. I can also ride no hands and turn and look completely backwards without veering. I guess the skill is about isolating what one part of the body is doing from other parts of the body. I can clip in and out in nearly any situation. And I can also shift while climbing an insanely steep hill. My technique is to pedal really, really hard for a second, reduce pressure for a fraction of a second, and shift with that reduced pressure. I've tried to teach it but not succeeded.