When the new taskbar applet landed in ede-panel, application icons were fetched in pretty standard way: inspect _NET_WM_ICON hint and decode image data, if application set it.
However, I overlooked one major feature of mentioned _NET_WM_ICON: this hint can support multiple icons (by different sizes), and modern GUI applications are starting to use it extensively. I added support for this in one of recent commits.
What are benefits of this? First of all, take a look at the provided picture:
The first image is natural sized (16x16) provided by application and the second one is explicitly scaled, which was done until now. So beside cleaner icon look, we saved a couple of CPU cycles that would be wasted for unneeded scaling.