> Would there be any benefit of doing the above instead versus swapping the PK and UK on that table?
Probably not much on that table.
But sometimes you will want a primary key that uses multiple fields.
And, at least with INNODB (and, by the by, with SQL Server!) that has PHYSICAL implications:
With the InnoDB storage engine, the table data is physically organized to do ultra-fast lookups and sorts based on the primary key column or columns.
In other words, the primary key is placed FIRST in the record layout *AND* forms the basis of the B-TREE organization of the entire table.
SQL Server takes great pains to emphasize that choosing your primary key can make a huge difference in performance. MySQL isn't quite so sensitive, but it can still make a noticeable difference.