We don’t create tags and just leave them lying around in case someone needs them. The purpose of tags is to group related questions together, so tags get created when we notice we’re getting more than a couple questions about a topic.
Tags not associated with any question are automatically destroyed at 03:00 UTC every day. If there is a misspelled tag like gramma, or a meta tag like sentence, all that has to be done to destroy it is to edit all questions it appears on and wait. Almost all of the tags you see in the list with zero questions are synonyms of other tags.
In my experience, if you want to get a new tag to stick, find about 10 questions it belongs on to tag with it, and then add a description so people understand what it is for. A lot of terminology people use teaching EFL is regional. One person’s ‘continuous’ is another’s ‘progressive’, so if there is another term that people use for a tag, creating a synonym might be worthwhile. Also, as an aside, prefer the plural for tags that have the form of a countable noun phrase (Should we not use "verbs" instead of "verb"?).
There needs to be a reason for the tag other than “it is something that exists in English”. If we have a set of questions that need to be grouped with will-future that are distinct from questions about future tense, there’s no reason to not create the tag. Tagging questions correctly makes the “related” questions in the sidebar a lot more useful and makes it easier to find and connect duplicates.
