When I get a new snake it goes in quarantine (ofcourse!!!) for a couple of months. In that period I take a stool-sample to the vet and if it's necesarry (after the stool-sample check) I take the snake to the vet for a check-up and treatment.
Every 6 months I bring stool-samples of my snakes to the vet just to be sure nothing is wrong.
I take Monty to the vet more often because he has a problem with his lungs. So every few months (depending on how he's doing) we check his lungs.