Software updates require a restart, but that's not what I'm thinking of when I consider a power down. I'm thinking of the scenario where you take explicit action to power down your machine and leave it powered down. I power down my machines before going on vacation, for example.

Even when you power down or restart a Mac it remembers all the applications you had running and all the application windows and it re-opens everything so you come back to everything just the way you left it.