I find the placebo effect makes everything sound better when the grills are off. I put the grills on whenever there is a risk that visitors might be sneaky cone pokers or port fondlers.

Oddly enough I never feel any urge to remove the grills on the QS8s. Then again QS8s have 4 grills per speaker so we're not talking immediate gratification there.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8