Other than to pass time?
I mean does it increase the time Well Rested/Lover’s Embrace will stay active?
I know it doesn’t restore more health, as sleeping a single hour appears to restore 100% of lost health, and it doesn’t appear to have any other benefit, does it?
Answer
As you say in the question, there is no additional benefit to sleeping more, other than passing additional time.
There’s no length increase to buffs, for example Well Rested (which lasts 12 hours from awakening regardless of time-slept).
Attribution
Source : Link , Question Author : CoqPwner , Answer Author : Jeeva
