(For MS SQL server)<p>If UUIDs are not sequential (i.e. random), there could be performance problems to used those as PK with an underlying clustered index (CI).<p>The CIs work best with sequential values.<p>Inserting a random value into a CI will certainly cause: (1) touching of many pages (write amplification), (2) index fragmentation, (3) page splits, (4) pages being half-full.<p>Furthermore, if you have other indexes defined on the table, these problems apply to these indexes also.<p>This of cause depends on data quality and data volume.<p>For the "mostly-append" fact tables, I would advise against using UUIDs as PKs with CI.