I have to be honest, I just never get the people who like to go onto the pee-wet lav floor with socks and then go back to their seat with soaking wet socks. That is not for me. Putting on shoes takes too much time and effort and ruins any attempt at going back to sleep. Slippers are a must to be able to sleep on flight. An extra pair of socks is easier to pack (and takes up less space) than slippers also..