Difference between "Show palette for one action" and "Show Palette of Macros"?

The Show Palette of Macros action gives you access to the Conflict Palette facility with your choice of macros. You can choose any selection of macros, and selecting a macro group is just a short form for selecting the contained macros.

The Activate Macro Group action and its variants, including Show Palette for One Action allow you to explicitly control the activation of a macro group. The palette you get is the macro groups.

I could, but I'm not going to - it ads clutter and confusion that would almost never be warranted. Set the macro group to Show Palette Until or Show/Hide Palette When and don't configure any options, which more accurately expressed what you are doing and allows you to configure the palette.