I would think if their healthy and you have no concerns then once when you first get them should be sufficent.

I have had my bp 3 yrs and he has been there 3 times, once when I first got him, worming, last year because his eye looked funny. Other than that I feel no need to disrupt him and haul him into the vet for no reason.
I could be wrong so hopefully others will chime in

My bp goes to a herp vet and he has never mentioned regular visits.