I’ve personally found the Play Raw threads to be the most helpful regular feature of this site. I love that I can take a good picture that I’m struggling with, upload it, and have a dozen different people process it in different ways. I’ll scan through the different treatments, and if I see something that catches my eye, then I’ll download the PP3 and figure out how they did it.
After RawTherapee documentation, it’s probably the one thing that has helped me learn to be better at processing pictures. I thought there would be no way to get a nice looking sunrise picture in RT, but my recent thread proved me wrong. It’s turned me onto some previously hidden powers of the software that I now have to figure out how to exploit in future pictures.