<p>The question seems to be answered in comments by <em>@whuber</em></p>

<blockquote>
  <p>It might be good to know that language tags allow the system
  automatically to markup any code blocks in the question and any
  answers. For example, this is how various keywords and other lexemes
  get different colors for <code>R</code> code.</p>
</blockquote>

<p>and <em>@gung</em></p>

<blockquote>
  <p>Cleanup is always appropriate. I edited the excerpt to include usage
  instructions based on the <a href="https://stats.stackexchange.com/questions/tagged/r" class="post-tag" title="show questions tagged &#39;r&#39;" rel="tag">r</a> tag excerpt.</p>
</blockquote>

<p>Tags are helpful for syntax highlighting. There is not much harm in having multiple tags (but we should merge redundant ones), while hunting and deleting tags is time consuming. Creating tags is relatively easy, so we'll never have a perfect tagging system, so better think about it in terms of their utility, i.e. to improve usability of the site (search, syntax highlighting, "followed" tags etc.).</p>

<p>Better alternatives to tag-hunting are:</p>

<ul>
<li>clarifying the tag excerpts and descriptions, so it is clear when the particular tag will or will not be useful,</li>
<li>merging tags with their synonyms, to improve search and indexing,</li>
<li>re-tagging questions by adding relevant tags and removing the irrelevant ones when possible (abandoned tags are auto-removed by the system). </li>
</ul>
