If you open and close your pc frequently throughout the day, it's better to keep it in sleep mode bcz everytime you shutdown and power on there is a surge of power that will deplete the life span of the laptop, but for keeping it off for a long time like overnight, weekends mnamn,it's better to shut it down. [If you really need to put it on sleep mode overnight (not to loose any work on the pc), just remove the battery plug in the charger and leave it on,then put it on sleep mode]