It was received knowledge thet SQL Server (at least) would have problems if you had a massive index on randomly generated UUIDs.

By the time I compared UUIDs to sorted UUIDs (in the special pattern that was supposed to work for SQL Server) and ints, however, I didn’t find any difference in performance.

Perhaps by the time I tested it had been fixed, or perhaps it was only an issue in certain circumstances, but never an issue with a few million rows for me.