Less of a chance of the party to get out of control if you have it at a restaurant.

You don't have to clean up after a party if it is at a restaurant, better yet you don't have to clean up before the party.

If it is a small group and you want a real casual party having one at home is nice. On the flip side if you want to go expensive and fancy you can do that for less at home and you can practice with new recipes.