Nothing, as long as the participants aren't violating the law. Much in the same way that you don't get any input on how long my grass is, unless it happens to be a fire hazard.

Actually, to the contrary, through things like town ordinances and homeowner's associations it is very likely that you do get to have input on how long your neighbor's grass is

My city has an ordinance for a fire hazard. It's established as a specific length. My neighbor does not get input on that, it either is, or is not, a violation of the city ordinance.

I got fined by the city once for "harboring rodents" because my neighbor felt my grass was too long (and was also a dick).

If there is a loud party, call the cops.

And when the cops are getting called every week what happens?

Congratulations. You just invented "zoning laws".