I'll list some possible concerns. But first, can we agree that Mickey D's is probably not going to be a lot better at keeping this data secure than, say, my bank or government or insurance company? All of which have been hacked, repeatedly? Given that, the concerns don't need to be restricted to what McDonald's might do with that data, but what anyone might do.

1. By combining and correlating this data, a stalker doesn't even need to leave his chair to have a very good idea of where you will be. "AI, when is the best time and place in the next week to find my ex alone?"

2. Startup idea! A dating site that gives an involuntary set of ratings to every single -- never mind, every human -- within 50 miles of your location. Healthy habits on a 0-10 scale. Willpower. Financial resources. Willingness to spend. Emotional vulnerabilities reflected in external behavior. Litigious or doormat? Look up someone you're interested in, or give a rank ordered listing and recommendation of how to meet them based on their purchase history. (eg they spend a fair amount at REI. Or perhaps they spend a lot but seem to collect gear, never go on trips?)

You may be proud of the results of your diet, but you'll have to wait until it gets reflected in the data before anyone will return your calls. If any information is wrong, you have no recourse to correct it. And if an undesirable's data gets mixed in with yours, look forward to dying single.

3. Scoped to a single company having the data: a lot is about the asymmetry of the information. You'll be charged more, get less, be marketed to when you're most vulnerable or in the most need. Imagine the extreme: a $40 bottle of water at a concert or a fee to see a doctor a bit sooner when you're bleeding out. Only not that obvious, it's only a little bit at a time so you'll never complain and never notice (until maybe one day you will). The rich get richer and the poor get dead. We don't have comparable information on the companies to make them compete more or more fairly, and the Grand Opening of Jimmy's Burger Shack will need to convince everyone that they have better enough burgers that it's worth the premium price because Jimmy's doesn't get the Big Data boost that the McD's around the corner does.

And note that McD's is not using the data to make your experience better. It's using it to make your experience as bad as possible before it might cause you to stop going there. At least in any way that saves them money or increases the amount you're willing to pay. It's not even malicious, it's just the inevitable outcome of making numbers go up.

4. You really don't want to live in a world where everything is optimized to the bone. Your barista is stressed and pissed off all the time because they're doing the job of 4, which turns out to work enough of the time that only 10% of the customers stop coming, and it saves the equivalent of 11%. The only companies you can buy from are huge and surviving on surveillance and economies of scale. You have to drive your kids 45 minutes to school and 2 hours for a haircut, because having them closer together is inefficient. Not that your kids will be able to get a job without nepotism, because The Machine says that they cost more to train than the employer can get out of the existing single mother by forcing her into another shift. The world needs slack and long-term benefit, or we end up optimizing the measurable and pessimizing everything else.

Update: to be clear, I don't think McD's is being particularly scummy here. The question was "why care?", not "is this proof positive that Ronald is going to Hell?" With current legislation, they'd be dumb not to collect what they're collecting. I just think that this sort of thing can cause enough harm that a large group of people should work together to forbid this practice being applied to them. Everyone in the group doesn't have to work on it individually, we could pick people to do the work and call those chosen ones the "lovernment" or maybe something rhyming with it.