Wouldn't it be elevating your head, rather than your legs? Most sources I've seen[1] that discuss inclining your bed have your head be higher up than your legs.
I assume elevating the legs would increase blood flow to the brain? Elevating the head would presumably slightly do the opposite?
When your foot is swollen from a sprained ankle people recommend elevating it to "drain" it (I'm not sure if that is the real explanation for why, could just lower blood flow and not drain anything).