I know this has been discussed before, however, the discussion seems to be primarily focused on how it would pertain to Stack Overflow, with the apparent conclusion being that this is a sign of things being tagged incorrectly, rather than a need for something useful.
On other Stack Exchange sites, though, there are cases where this would most definitely not indicate incorrect tag usage.
For example, on scifi.se, there are many tags used to refine specific franchise tags. Some examples:
harry-potterhas many sub-tags such as
voldemort(149 questions), etc., as well as tags specific to individual books/movies.
star-warsalso has sub-tags including specific movie titles as well as
the-clone-wars, character tags (
darth-vader: 45 questions;
luke-skywalker: 27 questions, etc.), and franchise-specific tags like
jedi(66 questions) and
- Author specific tags are frequently forgotten. An excellent example is
george-r-r-martin, which should be used for every question related to one of his works (including Game of Thrones TV show, A Song of Ice and Fire books, and various short stories and novels unrelated to those titles). However, we have 181 questions tagged with the author, but 372 tagged with
a-song-of-ice-and-fireand 398 tagged
I know we have several users who make an effort to fix these when they can, but it is a difficult task, particularly since these examples are all very popular titles, especially for new users who aren't very familiar with the tagging system.
It would be really helpful if we could have the larger franchise and author tags listed as mandatory, or even implied, whenever the tags that are clearly always sub-tags are used.
It would be up to the individual community to very carefully evaluate which, if any tags would be set up this way, but it would make cleanup for those communities that have clearly-defined subset tags much easier.