Do we need one? They are nice to have
Why, and how often? You may want to dry camp on a longer trip during the hot weather. It's always nice to have at a truck stop or rest area just to be comfy while taking a break. We have a residential fridge but no inverter, so after about 12 hours it's nice to get it some electric power. If you want to run an ac unit then a 3500 watt with a surge to 4000 is gos to have. They are not too large and easy to transport in a truck bed or rear platform.
Built in or Portable. We have a portable unit. We like that as it does not take away from out bin space. As full timers, storage in everything!
If portable, what keeps someone from walking off with it? We have ours either on the truck bed or on the rear platform. We put a chain around the frame of the generator and have never had a problem.