Hi,
Actually depends how tight your timing margins are against .
If you have high-enough margins, it should be sufficient.
Else, coupling capacitance between metal fill shapes & some critical nets can cause problems.
We do not live in a perfect world, so some designs may have very tight margins, so, it is better to check how sensitive critical nets in the design are towards metal fills.
Probably shielding these nets could be sufficient - or use filler metals near critical nets as shields by tying them to ground.
Of course, this argument is mostly theory to me as in practise, critical nets I've had were always sufficiently shielded on same metal layer and sometimes above & below as well.
Best regards,
I-FAB