I didn’t even know this was such a big issue.
For this blog I’m not concerned, but this is just my rambling site and not a “real” site. However, for a real site there seem to be all sorts of issues. Apparently things can get yucky if you just use %postname% — at least at some point. Especially if you have a lot of pages (in a situation where I think pages means pages which are different from posts). Some of this gets into WordPress architecture issues that you’d both need to read the WordPress code AND understand the finer points of how databases work. I have to ponder this a bit. For now, this is what I found that seems most relevant.