PARTY_UID requires users to populate it with a unique value. The PARTY_UID column is used by several users to store a unique legacy system identifier.
The following are benefits to this approach:
a) Allows updating information that tends to change (Name for example)
b) Allows greater control of the data manipulation (loading, updating, exporting etc) processes in an automated fashion.
When new records are created through the UI for party, S_PARTY the default is ROW_ID as the calculated unique identification for Party.