I work for an exotics vet, and really the only reason to take a snake to a vet is if it's sick or to get a fecal done. Fecals should be done yearly, in my opinion, because they eat whole prey, which often carry parasites. You do have to take the snake in for an exam though, even if you just want the stool checked, because at least in the state of Indiana, it is illegal to dispense medication without the vet seeing the animal within the past year. It falls under the whole "patient-doctor relationship" thing. And ideally, you want to actually bring a sample in, as fresh as possible (fridge is ok if it will be a few hours, but no older than 24 hours), because lots of times, the snake has no poo available when we use a fecal loop.