We didn't vaccinate, so we just went every so often. Once before 6 months, once right at 6 months (when we'd just moved and tried to find a new ped, only to be threatened that she would fire us if we didn't agree to vaccinate... needless to say, we never went back there). A check-up at 1 year with the new ped and, after that, only when he had something going on or for a physical. DS has hardly ever gotten acutely sick to the point of needing to see a doctor (twice in 7 years), but he's had a few chronic things going on - allergies, hugely enlarged adenoids, that sort of thing.
If I had another child now, I'd take them for routine visits just because I love DS' doctor and would want her to know a new child as well as she knows DS. She's very tuned in to him and we have a great relationship. I would want that for any other child I had. When a person is in need of a doctor, it's much better for them to be treated by someone who knows their baseline, IMO.