Consider the scenario where it's you that's OOA, and you need to establish substantial positive buoyancy at the surface. Also consider if you're OOA or had to disconnect the LP host due to a free-flowing octo, insufficiently buoyant, and near panic. Someone's going to need to orally inflate that BC, and you better hope he knows how to do it with an octo/inflator. If he's your buddy, you presumably briefed him - but if he's not...
Yes, I realize that if you're OOA and properly weighted, you'll be neutral to slightly positive. Personally, I don't want to have to struggle to keep my airway above the surface chop while myself or someone else is doing an oral inflation.
This isn't a hypothetical situation. I've had to do an oral inflate at the surface using one, and it's not something that I care to repeat.