Refdesk is not a search engine, it’s a reference website. It is, in effect, a virtual version of the sort of thing you might find in the Reference section of your local library.
And like that reference section, it’s a bit of a mixed bag: curiosities, some useful stuff, and a whole lot of out-of-date material.
There’s a Google-powered search engine on the site, which I used to look up “self-publishing”. There were only two results returned, not counting the sponsored ads. One of these was from 2009, and the other was from 2000. Neither of them seemed relevant.
So is it all bad news? Not really. There are bits and pieces like Quote of the Day and This Day in History, which may appeal to some, a few search engines, such as one that looks on YouTube, and a huge repository of links to dictionaries and other reference sources.
I won’t be making this my first port of call, but it’s definitely a potentially useful site to know about. Just don’t rely on any statistics you come across on the site without checking when they were last updated.