I like keeping WBVs for at least the first 6-9 months. It's nice to have an "official" record of growth, and so forth, and since our doctors in the past have all been very non-controlling* (in the sense of allowing me
make the health decisions for my children! Imagine that!), so it's pretty low-pressure. I like to keep an eye on the growth curve, and while I can certainly do that on my own, if something were to come up, I'd feel much more comfortable taking my kids to someone with whom we've made the effort--on both sides--to establish a real relationship. After 6-9 months, I don't generally make WBVs, except perhaps once per year if we haven't been in for another reason that year. We are very healthy, FTMP, and it actually has happened--even with 3 kids--that we've had a year without any sick appointments whatsoever!
*and as a side note, IMO, a care-provider who is non-controlling and respects the parents' rights to make health-care decisions for their children is more important than a care-provider who agrees with me on any particular issue, even vax.