Yes, they scan that to make sure you get future flyers as if they don't scan it eventually you would be dropped from the mailing list
the manager at my local Joann's said to have them to scan it even if you don't buy anything
as soon as I get my flyer in the mail, I put it in the car in my bag so I always have it, just in case I run to town for something else I will have my flyer with me in case I stop in at Joanns
Craftybear