It will have your name and website sales place on it, so might bring in a few sales. Although I find most free stuff ends up in my round file eventually.
It might be nice to have the store's goodwill on the other hand, maybe they will stock your patterns in return?
Of if they get a lot of good feedback "wow, cute block!" you could become their 'regular designer', that would be something you could put on your website, or pattern if it came about.
Or give you a $20.00 gift certificate.