A friend of mine and I tested gas usage between leaving the tank on and only turning it on when needed.
The difference in gas consumption was hard to measure.
When he turned his on to heat up it would run about 20 to 25 minutes. So twice a day comes out to 40 to 50 total run time.
My tank ran about the same on the initial heat up but only ran about 5 minutes on the cycle. This happened about 5 to six times a day, hence, 25 to 30 minutes. Total run time about the same, maybe 5 minutes more. :h
Obviously it takes less gas to maintain temperature as opposed to heating from a cooler temperature. :S
Just for the record, we still turn ours on and off as needed when we dry camp and when we leave the rig for any length of time.
Just habit. :B