Sortable primarily keys matters very much for any DB clustering on them, e.g. MySQL/InnoDB and SQL Server. It also matters, albeit to a much lesser extent, to

Sortable primarily keys matters very much for any DB clustering on them, e.g. MySQL/InnoDB and SQL Server. It also matters, albeit to a much lesser extent, to others. Postgres stores tuples in a heap, but the PK is still a B+tree (ish), so an INSERT or UPDATE heavy workload will suffer somewhat.