It's an extra that might return half its original price when you finally sell the RV. We've had our MH for three seasons and have really USED the generator once, when we camped in Eastern Washington on July 4th and it was 110 degrees in the shade.
The rest of the time, the only hours we've put on it are for the monthly "exercising" task. I suspect it was the same for the original owners we bought the MH from, since the generator only had 48 hours on the meter after 8 seasons.
I had a medical problem two years back, and didn't get out to "exercise" the generator. It hasn't started since, and we haven't missed it. I have a feeling that something in the generator fuel system has been damaged by ethanol. The Onan owners' manual says not to use gasoline with ethanol added. It draws its fuel from the main tank. Am I going to drive miles extra (at 7 mpg) to find a gas station with non-ethanol fuel and then pay 50 cents or more per gallon for the privilege? Fat chance! I just wish I'd had the sense to disable the generator when we first got the rig.
I'll have to pay to get it fixed before we try to sell the RV, but (with luck) that's a couple of years away.