Watchers watch for many reasons, some not necessarily related to buying that item at all. Some watchers may be sellers keeping track of competition, or considering selling the same item and wanting more information about the market.
Interested buyers are interested in buying, though not necessarily your particular item or as soon as you would prefer. Some buyers may watch several of the same item prior to deciding which to purchase. Or they may watch an item that they perceive may be useful at some later point. The item might be part of a project that may or may not proceed until all the other parts are available. The watcher may be collecting a set, of which your item may be part. A watcher might watch an item to see if the seller lists other similar items that the watcher might be interested in buying. A watcher might be waiting to see if the seller raises or lowers the price.
Watching just means someone wants to keep track of an item and be able to quickly find it again without having to go through a search again.
What was the model number of the special part or battery that I needed for a particular device? I may not remember the number when I need to order a new one, but the part is already on my Watch List, so I do not have to remember.
