Say you are willing to go almost anywhere, but you MUST be out of Schengen by a particular date. Or you have a warrant for your arrest in a particular country.
Several search engines allow "anywhere" or some entire country as destination, but is there one that allows you to specify where you WON'T go?
And/or to specify places you cannot start from.
Filtering or scrolling through the results isn't always practical when the first umpteen dozen pages are the ones that aren't useful. (Like Bermuda being part of UK or Guam being part of USA.)
Azuon was a good choice for a while, but it has been broken for at least two years. ("There are no flights for your criteria"—when the criteria is from North America to Taiwan or South Korea during the months of May and June!)