what is the idea behind
If I save in this format they will appear here?
.ghx contain the same information,
.ghx is textual while
.gh is binary.
It’s also good for versioning since
.ghx is textual you can use this format to compare two Grasshopper documents using any text comparsion tool.
About the panel in your screenshoot, yes those files will also apear there.
where do I need to save
.ghx files in order to see them in Revit next to the player?
Is soon to say, but the idea is the user is able to add some folders where to look for those