Autocomplete provides suggestions of what you may want to search for. The main autocomplete spot in WSN is the search bar at the top. When a user begins to type a search term, the autocomplete suggests topic titles that begin with those letters. The user can continue typing their own search term or choose one of the topic titles to search. When the distance searching is on, the city to search a distance from also autocompletes -- this is especially helpful in cases where a city could be spelled different ways.

There are a few other minor spots that autocomplete as well, like the member list name search (autocompletes usernames), the owner name field on editing a topic, and the "To" field when sending a private message.

As of WSN 8.0, you can switch off autocompletes at Admin Panel -> Settings -> Switches. Be careful about this. The vast majority of people will want to leave autocompletes on, but if you're running a minimalistic site you may wish to switch it off to reduce the amount of javascript running on the page.