I agree w/ @Walter Roberson that I find the searching facility to be of little help -- I've got a bunch of things I know I've posted over the years and while I'm not even close to the volume Walter has, I never think to create a database of "things that might be useful again" so I rarely can find the post of interest even when I know it was mine.
The paucity of results per page that I've complained about since the introduction doesn't help; it just takes too long to page down page after page to make that feasilble --and the Q? titles, since are posted by the original poster are, as often as not, not even related to the real subject and remembering how it was posted is impossible.
It's the latter I think that limits the usefulness of the search engine as compared to googlesearch as much as anything, I think...it has a lot better chance the title subject matches the content and has a much larger viable population from which to choose. I've posited also since almost the beginning there needs to be more structure/restrictions placed on the title/subject.
Similar limitations hold for tags...the user doesn't have a clue most time -- I have a hard time coming up with those even for my own Q? despite 30+ year w/ MATLAB to make them really pertinent.