Ah, I'm only familiar with it from the first game where you'd initiate conversation and the NPC would become completely oblivious to absolutely everything else, so you could take everything in the vicinity and they wouldn't notice.
I'd worked on the assumption that it could just be used to direct their sight cone away from where your more light-fingered character wanted to be, though I didn't use it often enough to familiarise myself with its intricacies.
