Why did Path add sleeping as one of its five moment types?  

Path’s CEO Dave Morin answers this question on Quora:

We are now in the Post-PC, Mobile era. In the PC era we would often ask: are you online or offline? In the Mobile era this is no longer the case. You are simple sleeping or awake. […] Third, users tell us that they love getting our notifications during the day, but at night they would prefer if the notifications were not streaming in. Sleep also provides utility by turning off notifications while you are asleep. – Dave Morin, CEO Path

Interesting.