Yeah, person abuse is bad... We should absolutely strive to reduce it.

Seriously, as others have said, it's a good deal for scouts, spies, healers, summoners, buff-focused casters, and other classes who don't rely too much on direct attacks. Also useful for getting into spaces PCs usually can't. I don't think it would imbalance a game unless the player actively tries to think up outlandish tricks, but then again most rules or spells can be exploited in that way.