I think nearly all search tools (search engines but also search on most sites) would be infinitely improved if allowed to actually return no results or only a few high quality results. Instead of the current trend of returning lots of low quality results.
Sites could then suggest additions or changes to a search that have more results But suggest these vs showing them by default
This would make search much more useful for finding obscure content or for example mispellings (like misspellings)