Valves on a brass instrument need to be up or they need to be down - not somewhere in between. This is always the case with the Pat Sheridans and Carol Jantschs of the world. Their fingers never get caught in no-man's-land. You could say their fingers are opinionated. They have a very strong opinion about when they are being pushed down and when they are being released. I always learn a lot about technique when I watch great trombone players. When watching Scott Hartman or Joe Alessi play I am immediately taken aback by their slide work. Their slides seem to always be in one position or another and never seems to be en route. And this is just as true when they play Rochut as when they are playing Till Eulenspiegel.
Those of us with valves can learn a lot from them.