For the past several weeks (months?) there has been a lot of retagging here on Meta.SE, and sometimes other sites do tag cleanups too. Tag cleanups are useful, but they tend to bump ancient questions like this one from 2009. The problem is that, on the front page, all we see is "modified N hours ago by (name)"; nothing tells me the question is not otherwise active. Nobody there is actually looking for an answer to that question any more. But I clicked through, read the entire question, and only then noticed that it's nine years old.
While showing some indication of age on the front page would be hard, identifying tag-only edits seems plausible. The system already distinguishes between "true" edits (that count toward editing badges) and tag-only edits. For tag-only edits, would it be possible for the front page to show "retagged N hours ago by (name)" instead of the more-general "modified"?
In addition to making it easier to focus on answering questions, for those who are here to do that, I think this change would also make it easier for people participating in organized retaggings to track their efforts.
One might counter-propose labeling old questions somehow, but that seems harder to get right. Some old questions still require answers, so we'd need to take that into account, and how old is old probably depends on the site and the type of question. Instead of attacking that harder UX problem, I'm proposing that we handle the one kind of edit that we know doesn't change the substance of the question or its answers and make that easier to skip.
Labeling retaggings was requested in 2011 and declined at the time for technical reasons that no longer apply. (Everything used to be "modified", but we now have "asked" and "answered" and enough information for "retagged".)