<blockquote>
<p>Should we be merging our non-merged tag synonyms as a matter of course?</p>
</blockquote>
<p>Yes, we should.</p>
<p>The answer is in your question, which reflects the Stack Exchange guideline towards merging synonyms (<a href="https://meta.stackexchange.com/questions/70710/what-are-tag-synonyms-and-merged-tags-how-do-they-work">What are tag synonyms and merged tags? How do they work?</a>): <strong>&quot;All good tag synonyms should eventually be merged&quot;.</strong></p>
<blockquote>
<p>How should we define when a synonym is &quot;established&quot; enough?</p>
</blockquote>
<p>Let's say, give two months to users realize a synonym was implemented, and one additional month, so any objections can be made. <strong>If nobody presents concerns about the synonyms in 3 months, then, merge tags.</strong></p>
<p>So, for example, according to this proposal all tag synonyms in CV Meta should be merged right away, because the newest non merged synonym is from May/2015.</p>
<hr />
<h3>Advantages:</h3>
<p>One advantage of carrying on such mergings is to help users progressing towards tag badges (while just synonymizing them won't) and this is good because users with gold tag badges gain the <a href="https://meta.stackoverflow.com/questions/254589/when-did-i-get-close-vote-superpowers/254590#254590">close/reopen duplicate binding vote privilege</a> [only] over questions with those tags.</p>
<p>See this post on Meta Stack Exchange and the answer from animuson's. He says:</p>
<blockquote>
<p>Conduct the merge so there are no longer questions tagged with the synonym. Once all the questions have been retagged by the merge, your tag score will transfer to the new tag when the recalc runs and the old synonym tag will no longer be eligible for tag badges ... .</p>
</blockquote>
<p>So, for example, @gung should have already been awarded a bronze tag badge for the <a href="/questions/tagged/on-topic" class="post-tag" title="show questions tagged &#39;on-topic&#39;" rel="tag">on-topic</a> tag in CV Meta, because he has <a href="https://stats.meta.stackexchange.com/tags/on-topic/topusers">+231 score in 23 answers</a> and there are 101 questions 'tagged' <a href="/questions/tagged/on-topic" class="post-tag" title="show questions tagged &#39;on-topic&#39;" rel="tag">on-topic</a><sup>1</sup>, but actually it has two non-merged synonyms <a href="/questions/tagged/scope" class="post-tag" title="show questions tagged &#39;scope&#39;" rel="tag">scope</a> and <a href="/questions/tagged/close-reasons" class="post-tag" title="show questions tagged &#39;close-reasons&#39;" rel="tag">close-reasons</a>, so making it officially not 101 Q, but <a href="https://stats.meta.stackexchange.com/tags/synonyms">91 [on-topic], 4 [close-reasons] and 6 [scope]</a>. A merge would solve this.</p>
<p>'But how do we know if tags were merged or not?' According to <a href="https://meta.stackexchange.com/questions/281174/why-is-a-merged-tag-which-is-made-a-synonym-of-another-one-shown-as-being-used/281175#281175">this answer</a> from @Wrzlprmft, we should see no tags in <a href="https://stats.meta.stackexchange.com/tags/synonyms?filter=merge&amp;tab=newest">this page</a>.</p>
<p><sub><sup>1</sup>A user eligible for a bronze tag badge should have at least score +100 in the tag, a minimum of 20 answers in the tag, and that tag needs to be used in at least 100 questions. </sub></p>
<p>And as <a href="https://stats.meta.stackexchange.com/questions/2790/should-all-our-non-merged-tag-synonyms-be-merged-or-removed/4703#comment13033_4703">@Glen_b points out</a> merging synonyms can also cause dropping of redundant badges. For example, four tags which are synonyms are merged, and a user had bronze tag badges in all of them (100 votes spread in 20 answers for each tag) before the merge. Then, after the merge the user will keep only one bronze tag badge (for the master tag), and will gain a silver tag badge (400 votes spread in 80 answers in the master tag).</p>
