If I'm doing updates on a topic over time, e.g. game development progress updates, thoughts as I read through a book, etc. I would really like to be able to show them to people in the order they were made, instead of making them scroll down for a hundred years to start reading.
If there's no room in the UI for a button, it would be ok if there were just a secret URL parameter for this. But there should really just be a button at the top of every tag page that lets you switch the order.
Also user tag pages don't seem to paginate like everything else, which is pretty weird, and makes this feature even more necessary, since you can't even link to the last page.