If you choose this option build numbers will be picked, maintained and persisted in ClearCase using attributes. This is implemented using three attributes on The UCM project to which the target stream belong and one attribute on the component. Don't use this option if the account running the job doesn't have access to write new values to ClearCase. The attributes are:

On the UCM Project the target stream belongs to:
On the Component:

See more details regarding this option on the PCUM wiki.