Currently, we have a shia-sunni tag (16th most popular on the site), but it's not very clear what this tag is for, or why we would need it. The tag wiki simply explains what the Shi'a and the Sunni are, but it doesn't explain anything about the use-case of such a tag.
We already have tags for shia-islam and sunni, for those questions pertaining to those two predominant sects of Islam. From perusing the existing questions, the shia-sunni tag appears to be used mainly for Sunnis asking for a Shi'a perspective, or vice-versa (which often carries the necessary shia-islam or sunni anyway)
To me, this feels like little more than a meta-tag, which just adds noise to the tagging system. As described in Jeff's blog post
The Death of Meta Tags:
How can you tell you’re using a meta-tag? It’s easier than you might think.
- If the tag can’t work as the only tag on a question, it’s probably a meta-tag. Every tag you use should be able to work, more or less, as the only tag on a question. Meta-tags, like [beginner], [subjective], and [best-practices], are useless by themselves — they tell you nothing at all about the content of the question.
So the question lies: Do we even need this tag? If so, what should we be using it for?