To be honest, in my opinion, it doesn't help you get a place at university because virtually everyone's reference will be really good such that it doesn't act as a discriminator. But to not have a good one in the first place does put you at a disadvantage.
My point is that the reference (unless it mentions exceptional things/things you weren't able to mention on your UCAS form (like 100% modules or something)) only really brings you up to a 0 level. A bad reference, however, brings you down into the negatives.