The secondary benefit is marketing information. Where are your clients going to? Can you spot trends of spending linked to destination? All of that sort of thing.
The irritating point is that, to comply with the tax regs you HAVE to show the BP. At LHR last year (or year before!) I had left the BP in the lounge. So I told them the info on it but was refused and had to go back to get it. The agent merely read off the pass what I had told her but she HAD to see the pass for procedural reasons.