It's not really a replacement for the Pass through key action in the MIDI editor. It's only available in the Main section of actions. So funnily enough, if you'd be working in MIDI editor and wanted to use this or any other action from the Main section with a shortcut, you would still have to use the Pass through key action for it.
It may be handy for changing the focus while in the Main arrange though, when dealing with actions between different windows. Never used it myself so lack practical examples...somebody else?