The point is, is it harmful? The answer is no. Lip/mpc buzzing is just another part of proper embouchure development. Is it the same as playing the horn? No! Only playing the horn is like playing the horn. Is the pencil exercise harmful? Are long tones? Pedal tones? The answer is that done correctly,no. They are all just facets of embouchure development. Here's a link that I find/found helpful. The Trumpet embouchure - how to buzz As an aside, the poster has been MIA since 2009!