Coincidentally, I came to the forums with the intent of posting questions about mute~ too!
1/ I am also experiencing the situation where mute~ does not appear to make any difference to CPU load, even tho' it seems to cause audio processing to stop. pcontrol with its enable message does make a major difference - with the latter, a test patch running at 60% CPU dropped to about 9% (however, I'm puzzled by why it's even as high as 9%, given I disabled pretty much everything in the patch...).
2/ Mute~ only appears to work as stated on the tin in very small, very simple patches. So I'm wondering whether there are situations/particular objects/preference settings that affect its behaviour.
3/ It *seems* as if mute~ messages do not work if they are sent remotely (e.g. via a send/receive pair), or from inside one subpatch to another subpatch. Is this true? The MSP Reference says that mute~ doesn't work inside bpatchers - perhaps it doesn't work inside any patcher except the top level one?
4/ Something that I'd suggest ought to be altered is the fact that mute~ causes an almighty thump when it's turned on/off. This can, of course, be hidden using judicious volume controls and delay messages, but since the object only has one function, you'd think it would do it without assistance! :-)
5/ One final point, the original mute~ help file, and the revised one here, both confusingly state that the pcontrol disable message "disables all objects (i.e. MIDI)". I believe that it disables MIDI objects, but not *all* objects (to test this, I wrote a little patch to do basic arithmetic - it worked, even while 'disabled').
I checked out one of the things that was puzzling me. Mute~ does indeed not work unless it's *directly* attached to the patch it's supposed to be affecting - so no send/receive or send~/receive~ pairs, no messages from inside one patcher to another etc.
When placed correctly, it works fine! In fact, in a test patch it worked *better* than enable/pcontrol: the latter reduced a load of 60% CPU to about 15%, the former reduced it to 9%.