What's the difference between post-process in the project settings, and post-process volumes?

This is likely a very simple question, but I’ve been playing with post-process volumes, and I see that a lot of settings are duplicated between the volumes, and the default post-process settings in the project settings menu- is the intended workflow to ignore the settings menu entirely, and manually apply all effects via volumes in-level?

You usually want a PP Volume in your scene. It has all the relevant settings in it and you have more control over it’s flexbility. You can also have various post volumes in your scene with differnt effects. When you set it to “unbound” it will affect the entire world.

See the Content Examples project from Epic for a detailed walkthrough, also the documentation is of big help for understanding volumes:

Ooh that’s super-helpful, thank you! Should the PP settings in the project settings window be ignored/turned off by default, or can I just ignore them altogether assuming I have a global process volume somewhere in the level?

I think, I’m not sure, that the one in settings designates how certain volumes are used within the game. Like for highlighting objects when the player looks at them etc. Whereas the volumes themselves are always active.