It reduces condensation. And of course hydronic heating and diesel generators run off of same diesel tank. Get truck stop diesel. They're bigger, have high volume of diesel business, and it will be fresher. HWH air leveling is common on CCs.
Proper way is to leave engine on, set park brake, hit panel twice.
Then okay to hit dump button. Good idea to dump the air before storage, to avoid uneven air loss corner to corner. Fully dumping the air will not damage anything. LP is very safe substance. No pilot lights.