There's one other time where a Multiform is probably more appropriate than OIHID -- when the skillset is radically different. This is one way to handle "chipping" skills in the cyberpunk genre, for example.

Of course, part of the reason for that is that I'm a total geek when it comes to not allowing anyone (PC or NPC) to take disadvantages on "rolling" skills (skills that involve a roll), excepting the Darn Good Reason(tm) standard.