The register printed coupons I get have plenty enough digits on them to be individually tracked. I imagine they are, but I haven't tried to figure it out. Several uses do come to mind, tracking the campaign, linking credit cards, things like that.
If you pay cash they can give a coupon to have a second go at adding purchases to your history, what's better is they're things you thought you'd kept off your history - it's cool in an evil overlord sort of way.
I find that Tesco give coupons for whole cart discount at a purchase price of about 25% above our average spend. That's a good tactic too.
