The advantage is that unlike "disease" or "contact lens" or "vt" residencies which essentially stick residents in those clinics for a year, primary care residencies usually provide extra exposure to all disciplines.
If your goal is to work for the VA, that's fine. But if your goal is private practice (as mine was) then it is much more helpful to know a bit of everything instead of being an expert on MEWDS or post PK bitoric bifocal RGP fittings.
In practice, I have found my residency experience to be invaluable.