It won't nessessarily return just any term for just any search; it's kind of hard to explain briefly..
Well, the "reason" for the box is to clean up how URL's look, and how url's are fed to the browser/client requesting them; it's just that the "cleanups" work well with search engines; the initial cleanups in previous code where based off of proven techniques...
If you surf around UBBDev about 2-3 years ago you'll see me talking about search engine spiders and a paid search engine hack that I was using at the time; this was just before SE friendly url's where introduced into the feature set (of at least classic; I don't know when they where put into threads as I wasn't a threads6 user).
