I've looked through the Help file, and the Gui, and there's one feature I would really like to see included that isn't presently available.
When I set 7z to extract or compress while running in the background (low prority?), I would like an audible sound to execute to notify me that the task has been completed before it simply disappears from the taskbar or system tray. In the GUI/Context Menu, if there was an option that could be checked or unchecked to play a sound file upon completion, it could allow users to choose to enable or disable sound when running 7z only in the background. An option to allow a user to choose any .wav file, like those found in the Media folder in the Windows Operating Systems, would allow users to not only choose the sound they prefer, but also eliminates any need to include a wave audio file with 7z builds.
Again, this is only for when 7z is running in the "background".
Apply this patch to the 7zip version 9.22 source code and recompile. It will play an audible system beep if the action completes while running in the background.
+1 for all future versions (GUI)