I used to work at a body shop and you just can't be impatient. If a panel is relatively flat in one direction then definately use a block and work in a hex pattern. Part of the results in working the edges out has to do with application of filler as well. The smoother it goes on, the easier it is to "keep" it smooth as you thin it down.
In any event, I would stay away from entire panel application as it is un-necessary and the end result will have more filler involved that wanted. With that said I always "over cover" to make sure the entire affected area is covered, then plan on thinning it down till the un affected metal at the outer edges begins to show thru.
