I think you are a bit confused on the point of tags on Stack Exchange.
A tag is a word or phrase that describes the topic of the question. Tags are a means of connecting experts with questions they will be able to answer by sorting questions into specific, well-defined categories.
As a general rule, you should avoid creating new tags if possible, and new users are not allowed to create new tags.
I know that the philosophy of when to create tags varies a bit across the sites. In SF&F, we have a general rule that you don't add a tag for one-offs where only one question exists in the category, particularly if it's covered by other tags and our rule of thumb is "Can you imagine an expert on the topic of the tag clicking into it to find questions they might be able to answer?"
yoga makes sense because we have many questions on the topic, and there are experts in it.
wheel-pose makes a bit less sense because it is not a common question, and it's doubtful that there's someone who has specialized in it.
It's a reasonable question to ask why we might restrict creation of new tags. First of all, it helps reduce clutter, tags that are only used once, or even never used after reclassification. Secondly, it helps prevent tag decay where the tag is used once for one case (where it might be valid) and months to years later, someone else sees the tag name, thinks "Oh, that name fits my question", and provides an incorrect tag.
I don't think these new tags would be useful to the site, but I'm willing to hear your arguments otherwise. :)