I own a Bigfoot 27' with LP generator built in. I would say it is more or less used randomly or seldom. That is only because I usually go to sites with full hookups.
If I was going dry camping I would bring along the Honda EU2000i to run more than 1/2 hour. The Onan Microlite does suck propane at a rate much more than the Honda uses gas, and is louder. Of course you can run it once a year and it never gums up! Just ran mine the other day for the first time in a year and drove around with it and the AC on while I took it to the car wash.
You can pull up to your campsite with no hookups and it starts pouring rain and 85 degrees........you just push the button and fire up the Onan and the AC while not getting wet.
Also great if you just want to run the microwave for 10 min at the rest stop for a quick lunch, not having to drag out the Honda and cables and have it get stolen.
If I ever got another trailer it would include a gen.