People can choose how much they eat. Pets can't decide for themselves and will always eat if there is food in their bowl. For people, a lot of the times it's an addiction and will definitely lead to health issues, so even in that case it's something to worry about. Food brands occasionally need to present goals in order to reduce sugar, salt and fat in their products. Don't get fooled by appearance, pets need to be taken care of and the same goes for people.
At least in my experience, this isn't true for all pets. I ever only had one dog that ate all the food in her bowl no matter what. All the dogs and cats I've had besides that one, including the 2 dogs and cat I have now will eat until they're full, regardless if the bowl is empty, and then come back to it later.