<p>I would usually avoid adding the tag unless there was something about the <em>question</em> that made it Bayesian or at the very least where a Bayesian approach was <em>notably</em> natural or obvious.</p>

<p>Note that adding the tag carries a degree of implication that the OP sought (or should have sought) a Bayesian answer -- if a non-Bayesian approach is just as reasonable, then I would not add the tag, because it could imply other answers (including answers that have not yet been offered) have mistakenly taken a non-Bayesian approach.</p>

<p>Similar considerations would apply when adding a tag implying a particular methodology when some other methodology might quite reasonably be used.</p>

<p>There can be something of a grey area; if you're not sure, one thing you could consider is to ask the OP if they're happy to have the tag there.</p>
