Mark told a very illuminating story from his aikido practice.
A Japanese master was visiting and supervising the students at the aikido dojo. He didn't speak good English. He would tell the pairs of students to start their work - they did - and then would call "stop". They would all stop and look at him. This happened a couple of times. The master shook his head in frustration - "no, stop like frozen water."
So the master then told them to start their work, and then yelled "stop!". All the students froze in place.
He then said "if looks silly when stop like frozen water, technique probably not correct".
Mark told this story while talking with a woman who was working with her horse on halting from the walk and trot - she said that she'd been taught to lean back, drive with her seat and squeeze with her legs to "drive the horse into the bit" (words of her trainer) so that the horse "could get its hind end under and lift its belly". She was beginning to question this - she said it made no sense to her.
Mark said that, if you removed the horse from under you at any point in your riding, would you be in balance or would you look silly? If silly . . . probably bad technique.
Mark said that horses can learn to associate any cue with any desired action - but many of those cues and rider actions just make the horse's job harder than it has to be. Leaning back puts the horse out of balance, driving with the seat cuts the horse's energy flow in half as well as creating a big block to movement in the hind end, and creating a brace between our hand and leg just makes the horse's job harder.
Our job should be to make it as easy for the horse to do a requested action as the horse could without a rider, and to have what you do together with the horse be as natural and balanced as when you do it on the ground and to have the same feel. Direct the horse, but stay out of the way.