The last two instances are extremely bad practice, but, as with any bad practice, they do happen.
Merge Replication and the GUID column With Merge Replication, each table that is part of a publication requires a UNIQUEIDENTIFIER column.
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For example, take a table named Merge Me in database QTuner.
This table consists of a primary key and does not require any additional changes to be used in transactional replication.