It makes a difference. Purely outdoor cats die sooner because of food, parasites, and illness, along with predators, cars, and accidental poisoning. Mostly indoor cats that are let out are fed at home and go to the vet. But they’re still at risk from cars, poisoning (ie, say a neighbor planted some lovely lilies and your cat goes to sniff them - lilies are deadly toxic to cats and just biting a leaf can kill them), and larger predators if they aren’t supervised.