:shakeheadAlexMDiver:Leave it on the boat unless the dive needs a long surface swim. The thing just gets in the way.
As an instructor, you ought to know better.
Haven't you ever seen a student who was away from the boat, and out of air?
Haven't you ever had a long surface swim, either to or away from the boat, and preferred to reserve your tank for underwater?
Oh, yeah, a snorkel is a real nuisance. :crossbone

But then, so are the weights, BCD, and regulator. Then, my fins hurt, too...
The snorkel is backup safety gear. It is bad form, as well as a dumb idea :11doh:, to leave it behind.