It would depend on the setup, you could have it as no whispers, to give maf three periods of no communitcation (day party day), or have whispers and make the maf take chances of leaking and such.
But then, maf will just pick a random person to kill by voting, other groups will just do whatever they do... just seems odd to me. Still +k, though, because I'd like to see how it works in practice.
It means they can't communicate strategies, so mafia can't tell their partners what they need to do. And I reckon there would be something in red at the top announcing it's a party, so mafia don't start talking thinking they're alone, only to be surprised.