What this is about is content that gets moved to different addresses. Recycling addresses isn't that good either, but also not that bad. What is really bad is

What this is about is content that gets moved to different addresses. Recycling addresses isn't that good either, but also not that bad. What is really bad is when there is some document/resource/content that is linked to by others (be it in other web pages or in bookmarks), and then that document changing its address, as all those references now don't point to the document anymore, even though the document actually still is available somewhere. An address being reused for something different isn't really all that much worse than the existing references leading to a 404. But either of those is bad if the original content is still available somewhere.