<p>I agree with @whuber that the fact, <em>in isolation</em>, that a tag has only ever been used a few times is not necessarily an indication of any problems.  It does seem reasonable to me that rarely-ever-used-ness correlates with other properties of tags that may indicate some issues that should be addressed.  What I take from these facts is that each tag that might be a candidate for being made a synonym or for burnination should be investigated.  If a reason other than low frequency is discovered, that tag could be nominated and the case for action could be made.  </p>

<p>As an aside, be aware that tags that are only on a single thread are silently discarded by the SE system after a period of time.  (I think it's 6 months, but I'd have to look it up.)  </p>
