I noticed a couple of people here seemed upset that the UR12 does not have an on/off switch, and I was too. But I have found that if you are powering it with a computer(USB) and not the 5v input, you can switch the unit off by setting the power switch in back of the unit to the 5v position. It’s better than having to plug and unplug the USB cable every time.
I know this is many years old, but I wanted to thank you for posting it. I didn’t like having the unit on all the time. In my case, I use a powered USB hub (KVM solution) so even with the computer off, the unit stays on. The 5 volt switch is just as good as an on/off! Thanks. I created an account just to say thank you! 
Does this not damage the microphone? I just got this interface and don’t want to damage anything