I leave it on, although that may change if I'm woken up by a notification. I have Silent Time on my Note 2 to turn off its sounds between certain hours, but the Gear apparently can't be programmed like that as far as I can see.
I leave mine on. However, I break the connection between the Gear and the phone before going to bed to avoid notifications buzzing throughout the night. My phone is on blocking mode over night, except incoming calls (you never know when an emergency might happen).