Well with the e ink display it uses zero power to hold the screen saver once it pops up . although I swear that I get phantom page turns in the screen saver sleep mode ....sometimes
. The only time I turn off complete is when I not going to use it for a day or so... but is not necessary . Although to extend the charge life when I'm not downloadimg a book or checking email I turn off the whisper net ... that makes a really difference in battery life.