I expect it will have effect fairly often - DISTINCT is something less experienced developers often add to fix their bad queries, and generally the first thing

I expect it will have effect fairly often - DISTINCT is something less experienced developers often add to fix their bad queries, and generally the first thing I do when I start to improve performance is to rewrite it to not have to do that. So if these improvements to DISTINCT make it more robust to bad queries, then a lot is gained. It probably won't fix all issues, but any improvements are welcome.