Having someone to pick up the groceries once in a while.
Having a second car in the driveway in case yours doesn't start.
Sometimes having someone put the driveway light on so you won't have to come in in the pitch dark.
Having someone to change the litterbox once in a while.
Having someone to either kill spiders or throw them outside, depending on whether you, or they, are a guy or a woman.
Having some to kiss when the New Years Eve ball drops.
Having someone to go to weddings with you.
That's about it, I guess. Don't ask about the disadvantages.