It might be because of the number of concurrent users you would have specified on the dbassit, which then would have internally callculated the RBS for you. You can always go and reduce the RBS. But remember you will not be able to remove the system RBS. Then also take a look into your init.ora file for the ROLLBACK_SEGMENTS that would tell you how many roll back segments are brought up when you start the instance. More the RBS, would not effect much the database, but make sure that they are all tuned for the operation, that is extent size and optimal number and etc.
Sam
Thanx
Sam
Life is a journey, not a destination!