There are some extensions (e.g. Extension:Math) that create files dynamically and then deliver those files to the user. Most extensions just create their files somewhere in $wgUploadDirectory, assuming that the location is accessible from the web. On private wikis this might not be true. Instead of direct delivery by the webserver the img_auth.php might be invoked. Unfortunately the current implementation sometimes makes it difficult or impossible to deliver files that are not part of the local filerepo.
Who would benefit
Any extension developer that wants to create files (images, pdfs, JNLP, xml, flat files, ...) dynamically and deliver them by a script entry point.
- img_auth.php could be improved (see also T153174)
- A complete new entry point could be created
- Some mechanism besides filerepo/filebackend could be created that allows better management (save/cache, delete/invalidate, find) of files created by extensions