1) Ear Training
2) Muscle Development (as long as your exercises don't teach pinching as a consequence)
I'd be careful over insisting on buzzing exercises. A little bit is good but I know people that take it way too far. I think singing exercises are actually A LOT more useful. I'm a trumpet player that has played professionally, was an all stater in high school and have had students play in the all state band. My bands always have what others have told me to be a beautiful brass sound. We never buzz mouthpieces in my band after beginner year.