The table column “term_group” is already part of the wp core but not used till now.
Creating term groups would help to create hierarchical taxonomy structures and better tagging. It could also help creating tag clouds for each group if those functions are implemented.
Examples of tag groups:
* to unite tags per language in a multilanguage blog and to show tag clouds for each language
* to use tags with more than one meaning – e.g. “plane”: a flying object, a canvas or a layer – in the right context.
For example the recipient of such a functionality is a blog in more than one language, a newspaper blog with different topics.
Or take my blog, about cooking. There I use tag groups to use same written tags with different meanings like “desserts” for desserts in recipes, desserts as a cook book category and desserts as a part of menus.
it is useful for the user to click in a book article on “desserts” and get further articles about desserts cook book without articles about desserts recipies and vice versa.
There are many more cases where same written tags with different meanings occur. Enabling a functionality to manage tags hierarchical enables more and better semantic descriptions.
Because the Tag Group plugin can not manage multi-level hierarchies of tags I use the Xili Tidy Tags plugin. But the column “term_group” is already in the core of wp so why not activate and use it as a core function?