My daughter said she doesn't have to share the spotlight with anyone else. She has Mom and Dad all to herself. She gets to have more one on one time....and isn't relegated to a specific day that she gets to be alone with mom or dad. Also...although she knows it isn't the most important thing...she doesn't have to argue with anyone over what to watch on tv, what games to play or whatever. If her friends are playing something she doesn't want to play...she said it seems easier to work it out with them and take turns.
She also understands that if she had siblings she wouldn't get to do as much dance and stuff as she does now. She said though on days when it is cold and rainy that it would be nice to have a playmate.