My rule is never go down, always take it out of the roof never grind the floor , you can knock the bunps off but that is it. Spend your time on the roof and walls.
My 2 cents
It's a good rule of thumb, but not always correct. Two examples off the top of my head are the SBC Pontiac head and the Mopar Stage VI heads. Dropping the floor on those is mandatory.
Counterintuitive, but true.
Of course, those are oddballs and it's almost always better to raise the roof and raise the floor as high as you can.