Theaters, weddings, etc. are absolutely not the only time you want to mute things. A very large number of people work in shared offices and operate their phones in silent mode all-day, every-day. I for one really appreciate that I don't have to think about what state my mute switch is in when I get home hours later and try to watch a YouTube video.
The common case is that your alarm is only ever set to wake you up in the morning and your timer is only ever set when you're sitting around, waiting for your dinner to be ready. It's very rare for you to set an alarm or a timer which will affect a quiet group environment.
I don't think that a hard mute-always rule is worth compromising the common case ;-)