And if you clear "do not replace...", a duplicated record will have a different UUID string.
Simple test with fictitious calcualtion:
UUID = timestamp and computer serial number
The timestamp will be the same for a number of records if you do create the records quickly enough.
Create a table with a callculated timestamp field.
Use table mode
Hold down the control+N key.
The timestamp will be duplicated for at least 10 records in my test...
It will be unique if the records are created a second apart.
What this means? I don't know...
This is also useful when importing records if you don't want duplicate uuids but may cause problems with relationships based on the uuid.
Only if you enable auto-enter options during import--which you would not normally due for UUIDs any more than you would for serial number PKs.