I'm not saying you should accept anything less than good riding. In practice, I make sure all of it is perfect for the sake of muscle memory.
However, when I go in to run, I'm thinking all about run fast and turn hard. I'm not thinking "Oh...Looks like my heels could be down a smidge more, and maybe my leg might be a touch too far back...Guess I better fix it."
To quote the people who yell at me from the sidelines, I'm thinking "HUSTLE HUSTLE. SIT. LOOK. KICK. RIDE ALL THE WAY. SIT SIT SIT!"
Kind of hard not to when I have such loud mouths telling me to do all that stuff...Gotta love them though.
I work for a reined cowhorse trainer right now, and he's in the hall of fame. We don't always get along but he did tell me this kind of thing. It's something both the trainer I grew up with and he have said, in different ways of course.
"Michaela, practice perfect, but when you're showing keep your head in the game and focus on only what you have to do next. Your body and your horse will remember what to do." (This was before a recent show where I was worried about my left leg, which has had a little trouble coming back from an accident)
I can see both sides of this argument, and see how both sides are legitimate.