On the off chance that you don't know what a thumbnail is -- it's that little preview of your document, photo, or video that appears when you are looking over the file before opening it.
Right now, there are many different, competing applications which want thumbnails of files, and they mostly implement the thumbnailing themselves. KDE has a thumbnailer for its apps. Gnome has one used by most of its apps, too. Still, there are a bunch of cross-platform apps which do their own.
Does it seem like kind of a waste? It is, and the FD.o guys have a specification to make thumbnails available to all applications with a single request. Since all FD.o specifications are designed to be cross-platform, that means that KDE users will be running their thumbnailing service, but a single GTK or Gnome app can request a thumbnail from it without having to start its own thumbnailer.
Gnome's compliant spec highlights the advantages of this new method:
Pretty much all the debate has settled down by this point and the major issues have been resolve. The specification can be considered to be complete, I guess.
- No need to link complex pieces of software into all the applications that want to work with thumbnails
- Possibility for thumbnailers of closed formats (which might have patents) to coexist with free software desktop applications that (just) want to display the files as thumbnails.
- Reuse of existing infrastructure instead of making all applications reinvent it
- Complexity of a LIFO queue is no longer the responsibility of the application developer