In this case it's a health issue - this is a bird with neurological issues (she can't balance well, can't really walk in a straight line) and deformed feet. But for all her problems she seems pretty happy. She used to sleep on our lower roost (she couldn't get up to the higher) but it seems that now her body's back in laying shape it's thrown off her balance even more (she's carrying her tail lower than before). I have a "baby" roost bar that's maybe 3" off the ground, and I put her on it after dusk, but she'll eventually fall off and start wandering.
She's actually quite high in the pecking order, has no issues holding her own among the older hens.