Auto-Notify filters allow you to screen new listings for search terms as they are entered onto the site by advertisers regardless of whether or not you are logged in. This is similar to performing a "search", but instead, the search "filter" terms you enter will be screening the site for listings that have not yet been entered. You can add or delete your Auto-Notify filters under your 'My Account'

When a newly entered listing matches one of your search filter terms you will immediately be notified by email. The email will contain the listing's information, as well as, a direct link to view the new listing.

So if there is a hot item that you and many others are looking for, you can get a jump on the rest of the site users by implementing a listing filter for that item.