Aye people watch for any number of reasons – it might be there are more than one listing of the thing you are looking for and you want to keep tabs on them all, but you might bid and win on one item before the other auctions close.
I do it to gauge the value and level of interest in things I might want to sell, or might want to buy at a later date. With some things I’ve bought I’ve been in no hurry, so I’m happy to watch auctions for months on end before bidding on one that is getting little interest. I bought a £10k piece of woodworking machinery for £600 that way, but waited months and months for the right one to come up, watching hundreds of auction go by selling at 4 -10 times the price.
from the items I’ve sold I’d say i’d usually expect one bidder for every 20 watchers, but whos to say anyone who bids was a watcher.