If you take your watch off for a few days, it may stop when the power reserve runs down. When you begin turning the crown to set it back to the correct time, it will start ticking again. And as the watch moves, the rotor will spin, adding to the power reserve. Even so, we would advise giving the crown a few clockwise turns to get it going again. So, while you don’t need to wind an automatic, you can, and it’s usually a good idea when you’re resetting your watch after a period of non-wear.