IMHO, grouping is nothing more than putting styles together that are similar or belong to a certain part of the document, like styles for a TOC, styles for an index etc.
In a long list of styles, grouping also helps to hide rarely used styles in a folders, which decreases the need to scroll in the styles pane.
Btw,, don't your eyes hurt with that color settings? Light grey on black or dark grey is the worse you can do to your eyes. Almost no contrast. Adobe's programmers must have been freaky here.
I understand the group and really appreciate this option.
However, I do not understand why in one document can exist styles with the same names and keyboard shortcuts?
When this is useful?
Colors interface - I have a similar opinion as you.
I don't think it's useful, but possible due to the group name which somehow extends the style name.
I only see a problem when those styles have different settings and you copy something from another document, where a style with the same name was applied, and that style is replaced by the wrong of the two identically named ones.
So we have a similar experience.
It seems that this tool is fairly specialized and should be called "Group for CSS".
And it has little to do with the "group" of what I think. When working with a document I want to better organize your view of styles in the document I'm working on, but using the current tool "Group for CSS" I create a completely new structure.
The problem is also in sync styles in different documents. It gets very complicated.
In the standard publishing work introduces more complications than genuinely helping the organization (by me of course).