So that it can do auto update when needed. You should be able to turn it of overnight, but do not turn it off for extended period, like a week or months.

Reason is you can get it updated when its idle and you can record your midnight show. Please, just dont switch off your electrical appliances like decoder or router. Thats not going to cause the electric bill sky high. Only air cond will
Why would you even want to turn it off overnight when the decoder has recordings to do.