It costs hardly anything (one formica counter, one enthusiastic wannabe Gok shop assistant) and it gives your shop an air of ooh-la-la. As The Devil says, it's simply another means of PR. Selfridges gets one. JL wants to be more like Selfridges, so they get one. HOF wants to be more like JL so they get one. Debenhams wants to be more like HOF, so they get one. (I don't know who comes after Debenhams.. I just know I don't want to go there.) How hard can this possibly be to understand?