When on park power and not wanting to use our propane, we just plug in a 1500 watt portable electric heater to keep the RV warm.
What a heat pump does in it's warming mode when it's warm enough outside for it to work well in it's heating mode - is use less park power than a 1500 watt portable heater would use - which could be important if you're paying for the amount of park power you use.
Of course using a heat pump to heat with is also more convenient than using a portable electric heater. Also, some folks won't leave a portable electric turned on while they're sleeping or away from the RV. A heat pump in heating mode would seem to be a safer way to heat for folks that don't trust a portable electric heater completely.