Reducing paint for brush use?

While many use airbrushes to apply their paint I understand some people still like to use plain old brushes.  I read somewheres a properly reduced paint will cover just as well as an airbrush, but the comment went no further.  Now, I am not looking to do total coverage with a brush, but I can see where small spots (perhaps a missed area of a cockpit and such) would be easier than going through the process of setting up the airbrush and clean-up afterwards.  So my question is, do you reduce the paint just as much as if using it for an airbrush?  If not what is a good ratio?  Or, unless covering a large surface is reducing paint for regular brush you just silly?

Brian