Depends on several factors.
But think about it this way. Universities around the AAA/AAB mark will get LOADS of applications from AAA/A*AA aspiring students - However many of those students are unlikely to Firm/Insure those university when they reflect on all their applications (Since for many people, a gap year may be more favorable than an AAB uni they put in to make up numbers)
All in all, they can be important but more than possible to get an AAB offer with lets say BBC/BCC & likewise predictions of lets say ABB - Since these students could be considered more likely to firm them (which is the most important part for them) than say an AAA/A*AA potential student - For example, I had a yearmate who got ABBC for AS but still got an offer from Warwick for an A*A*A/A*AA course.