A watch winder is a device used to keep automatic watches wound when that not being worn. If you have an automatic watch or self winding watch then it would be useful to have as it is more than likely you won’t wearing watch all of the time. You would definitely need a winder if you own more than one automatic watch.
If an automatic watch is left without movement it can lose certain functions that have been programmed such as time, day and date. Manual winding requires the crown to be unscrewed to set all functions again. The problem with manual winding is that it can reduce the life of the winding gear and also destroy the threads on the tube of the crown.
Now you know it’s probably best to stick with a watch winder. Speaking of which, you can grab one here for just £99 a pop (about US$149).