I managed teams at various levels (including Sundays many moons ago at the start!)
I always left 3 up top. One on the half way and two wide and a bit deeper.
Worked a treat for us and I did the same thing when I moved on and up.
Opposition often left 3 or 4 back when we did.
Did we concede more or less than we would have with everyone back?
Don't know, because we didn't do it so it's supposition.
I do know my Keepers loved it. Less bodies in there, less jostling, able to come and claim stuff in relative freedom. Most of it is mental. A mental boost. And always got the opposition thinking because oat didn't expect it.
We could have had 11 men back. But if they couldn't head , were nesh or midgets I never saw the point. Other than hoping they 'got in the way' they never achieved anything. Any half clearance would end up getting put back in anyway as there no out ball.
Sexton once told me, and it always stuck with me,
"There can be 22 players in there. But there's only one player going to get on the end of it. "