It'd be neat for most dungeons but likely rather hazardous for bosses or pretty much anything that cleaves. If the range was tuned right or if by some miracle SE were willing to put some effort into it's implementation then it could be quite handy though!

If it was my call, when following someone, I'd have Lily's movement AI ensure that when it's follow target is engaged in combat, she stays behind the target of her target. Effectively causing her to sit just behind the boss or such.

We can dream