Personally, it depends what the aim is. For my L119A1-esque that I posted above, I want it to look a bit used, so I only used thin coats and started handling it almost straight away. If the aim is for a new look, then I'll strip it down to the basics, or at least do a "proper" masking job. It will then be painted properly, starting with a sand/strip, then prime, followed by 2 or 3 coats applied according to the paint manufacturer's recommendations.
Ultimately, it depends what kind of finish you are after, and how OCD you get about it....