The feature is important because it allows EmEditor to be used for text extraction/data mining. Sure, EmEditor allows you to extract the entire lines where matches occur, but not just the matches themselves.
For example, suppose you have a document containing a load of URL’s interspersed with other text/HTML. The URL’s are in the format http://server.com/123/321, but you actually need them in the format http://server.com/321/123 (ie. the folder components have been swapped). With the functionality I’m requesting, it would be easy to write a find and replacement expression, and then extract just the URL’s in the required format.
The real-time/incremental update of the Output Bar with the results helps when writing the find/replace expressions as you can get a visual indication of what is being matched, and what will be extracted/shown in the Output Bar.
EmEditor already has most of the functionality built-in (ie. regex, incremental matching etc.), it just needs to be hooked up so that the matches appear in real-time in the Output bar.
Let me know if you need me to explain further.