You're right to point at performance as the main motivator for this setup.
The primary key is included in all indexes, including non-clustered indexes, so in some cases there can be quite a large difference between UUID and integer PKs in terms of index size.
UUID PKs are also more susceptible to fragmentation.
The primary key is included in all indexes, including non-clustered indexes, so in some cases there can be quite a large difference between UUID and integer PKs in terms of index size.
UUID PKs are also more susceptible to fragmentation.