title_body: When should I completely poweroff an eink device rather than putting it in stand-by?
upvoted_answer: The biggest issue is likely to be background network use. For example, Amazon's Kindles will continue to use Whispernet and/or WiFi in the background. Assuming you have turned those features off, you would want to power it off entirely only if:
  
  
  You plan to store it for a long period, on the order of months.
  You plan to open up the physical case for some reason.