It's polite to offer to cook someone dinner
Bob's mom works late and just got home, completely exhausted, but Bob hasn't eaten yet.
Bob wants to eat food.
Bob tells his mom that he'll make something simple for dinner, so she doesn't have to, then gets to work.
Bob comes up to his mom and asks her when they will have dinner, pointing to his stomach.
Bob's mom gets extra time to rest and enjoys the dinner that Bob makes for her.
Bob's mom doesn't get rest and wears herself out further cooking dinner for Bob.