Honestly it's just that how I've always done this, other ways seemed too noisy for me and breaking the flow of the game :)

That might or might not be due to the games we've mostly been playing on our LAN parties are coming from a bit different profile than "chill co-op" — more MOBAs or tactical / arena shooters. In those styles of games visual cues don't really help and not having the clear audio puts you at a disadvantage

The music is still playing in the background, though — the headsets are not 100% soundproof and you may still easily communicate via VoIP

Yeah, the "live talking" aspect without headsets isn't there, but I've found it doesn't bother me in the slightest. You still are in the same room, you get the "shoulder sense" of your team there, you still celebrate and have fun as one and lose as one singular organism, and that's the feeling I've kinda been chasing on my LAN parties and in my LAN centre