UDP vs TCP, might not care to know it was received. It may be evident/insignificant... later.

How it is different than if somebody responded "ok" or "sure" or any other similar message? Or is it also unwanted? How is the other side supposed to know that?

I wouldn't say it's much different, also unwanted in certain contexts. Perhaps not know, infer/make a judgement call. It's just as fair to consider it 'unreasonable' as it is 'assumed'; many things can be true.

The first world solution to their problem is Do-not-Disturb mode :P To keep the networking aspect: it's QoS! Helps me, can only blame myself for looking.