Hi James --
When the Go Button "Documents" folder contains an "Inbox" folder, it was typically created by iOS. That folder is an artifact of importing audio files from certain methods, acting as a temporary holding location while a file is being copied into the app. I think it happens (or used to happen?) primarily when saving an audio attachment from an email, like using the "Open In..." or "Share" options -- but maybe AirDrop and other methods do the same thing.
Go Button generally tries to copy files out of that folder to the top-level of the "Documents" when importing. But I can't say whether it is safe to delete the whole folder or not.
It would be safest to inspect the contents using the Files app, and try to determine whether your shows are using any of the audio files in that folder. If you do find that none of your shows are targeting a given audio file, then you can delete that file. (Always have backups!)
Brent