yes anal glands should not be drained too often, if a dog has regular appointments with the groomer, say every 8 weeks or so, it is okay to have it done then. BUT a groomer that does the glands on a dog on a regular basis is basically just checking, not putting a lot of pressure since he/she knows that they are being checked regularly.
When a dog is spontaniously emptying the glands that is not a trauma, that is a reflex. They actually in a way empty them to a certain extent every time they go potty, that is the reason the glands are there, to make it easier to make the big piles lol.
But no I agree, I wouldnt recommend draining a gland more than every other month or so, and if you have a dog that is not prone to have too much in them, well Id say once every 6 months is okay.
Marit