You'll be able to track devices if you have multiple APs deployed, or just detect whether someone is within a ~100-meter radius.
If you are shop owner, you could pretty accurately know where are your customers living.
http://lifehacker.com/how-retail-stores-track-you-using-your...
They use it to track your movements in the store. I forget the name of the most popular provider.
It's pseudo-anonymous in that they can get a unique identifier for your device (and thus know how often the device returns to the store) but can't tie it to your real identity without more information.
And given the mediocre accuracy of the technology it would be hard to correlate it with, for example, their point of sale system (e.g. 'device XYZ was near checkout 3 at the same time that John Smith's loyalty card was used there, therefore device XYZ is owned by John Smith').