Brian Baylis said:
"Most pro painters use at least two or three different spray guns to hose down the bikes. Generally one for primer, one for color coats, one for clearcoats. I really don't know why (OK, yes I do, but I don't see why it is neccessary). I use the same spray gun for everything! I've been using the same single spray gun since 1982 for every single coat on every single bike I've painted since that time. I even brew my morning coffee in the paintcup. ;-) As far as I know, I don't have a reputation for doing crappy paint jobs. I've never had a single problem with doing this and I wonder why so many painters have so many guns. I'm comfortable with my OLD Binks #26 gun. I can shoot a hole in a silver dollar before it hits the ground withit. Anyway, just wanted to say that, because I'm apparently some sort of freak."
It's certainly a luxury and potential time saver to have multiple guns. I own just one as well, a Sharpe detail gun (or Jam gun). You can certainly get by with one but you need to be more diligent with cleaning before color, and especially clear. The time it takes to sand out "leftovers" in a clear coat can let the gun pay for itself in very little time. This is for the production environment however, not the hobbyist.
I've looked into a newer gun, with my preference for gravity feed HVLP's from Sata.