Sleeping on the floor seems like a hassle if you have to get up every time the seatbelt sign comes on (assuming the FAs are enforcing the seatbelt rule).

Myself, I wear my seatbelt at all times, unless I need to be out of my seat for something. There's not much downside, but the upside is that (1) I won't be woken up and told to put it on and (2) I won't be permanently put to sleep by having my head smashed into the ceiling.