Hate calling it a mute switch... it's notification mute. Which is why I use it for that - as far as I'm aware, using the physical switch to mute notifications is the only means of doing so. Rotation lock at least has a software equivalent function.
On top of that, when I first got my ipad, I found myself locking rotation a lot more - now that I've been using it for as long as I have, there are still times I want to lock the rotation, but maybe once a day? So with gestures enabled, it's a swipe, a swipe, and a tap... not bad for something I do once or twice a day.
Notification muting though, I use all the time. Whether I'm in a meeting, watching a movie, listening to music, or just don't want to hear the click of the keys while I'm typing... but don't want the system volume muted, it's handy. That, and even more so for being in a meeting... I don't have to unlock the iPad to mute the notifications, which I'd have to do if I was just using the volume rocker to mute everything.
Glad the option is there though, but as long as there's no software equivalent for notification muting, that's what it'll be for me. Especially now with gestures enabled, paired with how little I find the need to lock the rotation.