Bear in mind, LJBF still equals rejection. Only, LJBF puts the responsibility of that rejection on the guy who initiated the intimacy (or the 'approach' if you like that term better). By defering to the LJBF response the guy has 2 options; he can either accept her terms of rejection and engage in pseudo-friendship as an obligation for his not wanting to appear 'shallow', or he can simply refuse any notion of future friendship and put the rejection responsibility back on her where it belongs in the first place - with her. Unsuprisingly, I'd reccommend the latter and there are very tactful ways of doing this that leaves you in a position of power and you walk away with your self-respect..
When a woman falls back on LJBF it serves 3 purposes for her. First, she is absolved of any liability for feeling bad about the rejection, if this even comes in to her thinking (she "tried to be nice to you"). Secondly she avoids coming across as a b!tch, both to herself and to her peers ("I tried to be nice to him"). Lastly, it puts the burden of the rejection on the man who initiated the approach by putting him into the difficult position of choosing whether to comply, and allow her to be aquitted of the rejection's implications, or to - unlikely - turn her offer of 'friendship' down and become himself a 'Jerk' for not allowing her the escape that LJBF implies.
At the time it seems a pretty simple solution to what amounts to a confrontation, but if you pick it apart a bit the complexities show LJBF to be a very useful and practiced tool for women. Half the reason so many guys become AFCs is due to this self-imposed expectation of an actual friendship (as if one could truly exist) when all an LJBF amounted to for her was a convenient 'out' of a confrontation. The guy deserves a real rejection, but far too many women are cowards in this regard. Not surprisingly many men assume her LJBF rejection is a "not now, but maybe later" equation and waste countless (and potentially productive) months, and many times, years in pursuit of an unattainable female who didn't posess the courage to give the guy a proper rejection and send him off to greener pastures.