Correct. It gives time for the staff (eg security) to decide what they want to do with you in the case of suspected theft or deception. You don't have to stop,

Correct. It gives time for the staff (eg security) to decide what they want to do with you in the case of suspected theft or deception. You don't have to stop, and sometimes I don't. It's not a legal requirement and any legal challenge is less cost effective for them if you aren't a suspect. The fact that isn't obvious, is not surprising but it is elementary, regardless of professions to the contrary.