<p>Although it is OK to use a relevant tag to couple question and answer it is not obvious that this is a expected behaviour of the site.  The tags are shown only under question, so the natural implication is that they apply only to the question, not to answers. </p>

<p>Although the idea is nice, searching only for answers which are analytical for example might be useful, it requires changes to SE engine. </p>

<p>Coupled with the very good points raised by @whuber, I think this tag does not merit the major intervention needed to justify its creation. Starting to use it on question by question basis seems entirely appropriate.  I think any new tag must first of all be used only for new questions and then if it shows its usefulness it can be applied for previous questions.</p>
