>>Agreed. Here the supermarkets DO store info about your buying habits. It's useful if you wish to use their online grocery shopping, when they deliver it to your door. You can have a profile already built up for your shopping basket and just alter it accordingly. However I don't use the facility.
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>The supermarket chains here typically offer members-only prices that are significantly lower than the regular prices. I gritted my teeth over giving them the ability to capture all my purchase history but the cost savings were too good to pass up.

Savings are in the eye of the beholder, if sufficiently gullible. That's not the money you saved - it's the money they would rip off you had you not confessed your name, rank, unit, location, eye color, blood group, skin sample...