Assigning a DEFAULT USER to a column is an easy and reliable way of identifying the person making an entry in a database. This information may be required; for example, when salespeople are working on commission.
Building a user ID default into the primary key of a table is a useful technique for occasionally connected users, and helps to prevent conflicts during information updates. These users can make a copy of tables relevant to their work on a portable computer, make changes while not connected to a multi-user database, and then apply the transaction log to the server when they return.
The LAST USER special value specifies the name of the user who last modified the row. When combined with the DEFAULT TIMESTAMP, a default value of LAST USER can be used to record (in separate columns) both the user and the date and time a row was last changed. See LAST USER special value.