The "rumours/information/comments' I've heard is it boosts your career prospects with respect to gaining a pupillage or it's the thing to do if you're going down the Bar route - it might be the latter. And that it's not particularly useful, like LLM programmes in general, if you plan on being a (commercial) solicitor. Obviously it's one of the most prestigious PG courses in the world at an equally prestigious institution. I'd wait for the more authoritative figures to see this thread before you take that as gospel though.
Out of curiousity, which university are you doing your first degree at?
I apologise if I have misread the situation but this smells like a 'tell me how great I am thread'. If you have actually been accepted onto the BCL you will know that it is the most prestigious post-graduate legal qualification in the UK period. And probably the world. It couldn't fail to benefit you. I went to Oxford and you don't get a look in at the BCL internally unless you get a first.
Your career prospects after completing the BCL are pretty f***ing good but I can't imagine this is news to you.
To be honest the level where it might matter is so narrow (considering candidates for it already have stellar academics from their first degree which will more than impress most employers) it's unlikely anyone really in the know will be on TSR.
If you want to be a barrister might be worth having a look around the websites of chambers you're interested in and see how many have it. If you want to be a solicitor just email HR. You could also try posting on RoF, though I think that's more solicitors than the Bar if you're more interested in that.
However, given you have managed to misspell 'boost' it seems the normally stratospheric standards on the BCL may be seriously slipping