HoudahSpot gets you to your files quickly by helping you narrow down your search until only the relevant files are left over.
Find by Example lets you refine a search using a prototype file: a file that has something in common with the files you are looking for. Drag and drop a file from Finder or from the search results onto a search criterion. It will update to match that file. You just told HoudahSpot:
I want files like this one.
For example: An initial search produced thousands of results. You know that the file you are looking for is a PDF. Drag any PDF from the results onto a “Kind” criterion. The search will now be restricted to just PDF files.
You can also nest the criterion in a “None of the following is true” group to negate it. I.e. remove all PDF files from search results.
Use Find by Example to find files by the same author, modified on the same day, sharing the same image dimensions, etc.