Reservations help the presenter budget for refreshments, chairs, and party hats. If you add or drop a guest at the last minute, so be it, but if your six in-laws decide to join you at the last minute, call and say so. Let them know if you have food needs or phobias - you may be the fifth vegan, convincing your host to go meatless this time. The layout of the house may make it painful for parties to walk in after the show's started. Roads close, house numbers confuse, travel times stretch like rubber bands.
New listeners are folk's lifeblood.
It's a cinch some folks will need change, so this is your chance to be a hero. Once you're there, you'll have a great time. Give your email if you have one, in addition to your street address. This is pure profit for the artists, and can justify the visit economically above and beyond what they made at the gate. If they're covered this time, let them know you're available next time.