A good friend of mine in Japan is a loyalty card junky.  She appears to have loyalty cards for every retailer he does business with.  The cards are stored in multiple business cardholders.  The flurry at the time of payment to secure the correct card can be an amusing and earnest dance.  However, when I question her on the benefits, except for a few, there seem to be minimal tangible benefits to her for using these cards.  This while the many retail businesses aggregate data on her buying habits.

From a different perspective, the rise of web page tracking with cookies