It is primarily used for thumbnails? I didn't know that. I thought it was used in the event recorder (frankly for 
  displaying the screenshots in the recorder GUI) and in sword25.

That is true, it was part of the event recorder branch and it's used in these places. So we have code that creates thumbnails for saved games (in thumbnail_intern.cpp) and code that creates thumbnails for the event recorder. This does tend to lead to some confusion :)