I know a few people that think disturbing anything at all is bad. One person in particular won't put his hands in the tank, won't disturb a snail, and would give you that look if he heard you even think of vaccuuming your sand bed. But I think anything in moderation is good. We had a lecturer talk about sand beds, and he said that you'll have anaerobic areas in your sand bed, which according to him is a bad thing but is natural. So bristle worms, sand sifting sea stars, cukes, sifting gobies, snails, hermits all stir it up somewhat. I don't see what it would hurt to gently vaccuum.