I prefer to use flat light colored paints. Unless you are needed to cover a model with dark areas with a light overall color scheme...such as a white plastic model with gobs of puttied areas you don't need total coverage. I simply mist sufficient paint onto the surfaces to get the final color sufficient texture to bite on. If you were doing a say...white or yellow scheme, then you'd want total coverage to get a consistant background.
The misting of flat will provide enough coverage to locate any flaws that need repairing before final painting.
I'll also use Mr Surfacer on occassion too.
Here's an example of one that would need a full primer coat prior to accepting a mostly white paint scheme.
