Unexpected things happen. What happens if you have sent out STDs but not invites, and something about your wedding changes (e.g., date, location, called off, etc.)? Call/email everyone? Send out another mailing?
I was talking to my FI last night about how frustrating my mother is being, and he said, well let's call the wedding off and elope. Now this wont be happening, but I got to thinking, what would we do if it did?