Retail shops of all sizes use video surveillance for security reasons. However, video cameras are good sensors for collecting customer data as well.
Video frames from surveillance cameras contain vast of information irrelevant for security officers, but valuable for store managers. For example, number of visitors entering a store, moving direction, dwelling time are all valuable data for store managers to respond accordingly, by managing stuff and adjusting product positions.
By contrast to other tracking methods (WiFi beams, passive sensors, mobile applications), video-based detection and tracking is far more precise, because sensor (in this case camera) captures information in the form of image sequences, where real positions of people and objects are recorded.