I'd do it again, but not for the money. I direct each of them to my website for re-orders. I also had some of my advertising hanging around and passed out business cards. I've booked quite a few baby portrait sessions from moms looking around at my web site!
So, the free marketing was worth it. A school carnival pretty much is all about the corner of the market that I do most of my shoots for. Families, kids, babies . . .
I felt like it was good for my business, NOT my sanity!