On Friday, there was a very polite person who at the secondary scan took your boarding pass, scanned it for you and then directed you to a free bay. The chap in front of me refused to hand over his boarding pass and was told it was mandatory. I also refused asking what it was for and they could not tell me, so I just walked to the next empty bay.
It is a bit like Boots or WHSimths asking for my boarding pass, its all about collecting (unnecessary) data.