Itzhak Pearlman says great words about how he practices. The main thing is they should not practice fast (unless they are pulling it off). I was pleased to hear him say what anyone with a working musical brain should have figured out. If you practice slow you are practicing the correct execution which leads to doing it right at any speed. Practicing with mistakes teaches how to play the mistakes, true about everything else from my daughter refusing to use a recipe for muffins (which surprisingly don’t come out the way she imagined) to people canceling people.