I guess we are starting to get busier on your forum eh!
Ok this would be a useful feature when you need to calm and maybe do some moderation clean-up. It is better than locking a thread, because it neutralising the problem user, while causing the least amount of disruption to the overall forum.
Next is locking a thread, which is often required if you have a mega multi-user spat. Unless it is easy to group mute, then this is essential.
I would favour a FREEZE topic, that is more attuned to dealing with eruptions of chaos, moderation is happening and is a temp process, the LOCK TOPIC is very definitive and possibly Admin only option - leaving Freeze to moderators and higher - but maybe I am splitting hairs here but I think it has some merit. Something to expand on later.
I see some users also want "ignore" features.
I am not sure an ignore features is a great idea tbh. It goes against the spirit of an open forum and also is again a crude feature to try and address what moderation shortcomings exist.
Basically it is a feature that is impolite by by stealth.
+1 for a Mute feature.