My watching list is often full, stuff that's BIN that I just haven't bought, stuff I want to save the pictures but didn't have time just then, stuff I thought I wanted but either found cheaper or it went for more than I could/would pay.
So when it's full and I'm browsing and maybe 20 pages into a category and I can't put something into watching since I just filled it....
Then I sometimes place a minimal bid which makes the bid list sort of an extended watching list.
Embarassingly enough one time my very low bid won and I missed the emails having completely forgotten the item. So I found out I won when the reminder to pay came through.
Other times I'll put in a bid to hopefully slow down the seller from selling off ebay.
Or a small bid on something I want cheaply but that I'm not really after. I've won a couple of those, maybe 5-6 in more than 10 years. Yes, I'm that cheap sometimes.
Steve B