I use it three ways.
If it's been a couple of weeks since I've painted, I'll put a couple of drops of restorer in the paint bowl, backflush, and clean the needle, before I paint again.
If my airbrush is "acting up" while I'm painting, I'll do the backflush then, too.
If my airbrush is not painting smoothly, and I've been using it for a month or so, I'll disassemble the airbrush and soak the parts in my glass pickle restorer jar. It has a gasketed top that screws on tight.
A clean airbrush is the secret to enjoying painting, so err on the "more often" side of your cleaning regime.
And be sure to thin your paint to the consistency of skim milk. Too thick, and you'll wind up fighting it, or having break down you airbrush and clean it all over again. Thin it with whatever that particular paint brand recommends.