The movement is that a rotor (shaped like a semicircle) rotates in the lock box and then winds around the main spring. The rotor is connected to the center of a full circle, and gravity lowers its weight, causing it to rotate as the watch rotates. In general, if you wear a watch every day, you don’t have to worry about it stopping. That’s because it moves around to sufficiently wind.
However, when you start to have more than one watch, especially multiple automatics, you can get into an attention problem. All these movements needing to be constantly wound. There are only so many watches you can have in a day. Most watch owners will spend a good amount of time each day manually winding watches. This does not mean spinning them around in your hand, but most, if not all automatics can be manually wound from the crown, just as a manually wound watch. This can become a chore, unless you really want to sit and remember to wind watches each day.
If you have a standby power indicator on your watch, it will be easier to work. It's a simple reading, more or less, showing how tight the main spring is, and your watch is power wound. The bottom line is that as your watch collection grows, you need to spend more time making sure they are wounds. So why not wind up your watch when you want to wear it? In fact, this is a good question, because some people may want to keep the watch's life by not always winding it around. The main spring is usually very hard and does not lose its specific tension. However, for older or more expensive watches, you may just want to wind them up while wearing them. Some watches have very complex movements that provide complete calendars, phases and other information. Once you stop the watch, you need to reset all the information, which can be tedious and need to be viewed online (e.g. with the moon phase indicator). Because of this, the watch should be ready when you want to wear it, and for the sake of accuracy, this is very important.
Watch winder rotates around its axis and tilts slightly diagonally. Most of them don't spin all the time and take a few hours off before they spin again. Most are powered by wall outlets, while others are powered by batteries for travel purposes. Of course, because there is a motor in the winder, people are worried that they will make noise. But even my own two very cheap clocks are relatively quiet and won't wake you up at night.
