That's been debated a few times. Some do. I don't. Seems a little tough on the generator (in my thinking) just to be able to run the AC before we get to the campground.
When I was racing, we only ran the genny at the races once we were set up and the generator never gave us one bit of problems for two hard years.
2015 F350 6.7L Lariat CC LB
2016 Vengeance Touring Edition 40D12
Former Forest River Campers:
2004 Puma 30FQSS
2010 Sabre 31QBDS
2014 Work & Play 30WRS