My take is you would want to prevent a maxextents error from occuring by setting it high - I usually set it to unlimited for rollbacks, and then manage the rb segs in other ways - by properly sizing them on creation with the transactions and monitoring the tablespace/datafiles via scripts or processes. If you tailor the maxextents to your 3G now, then at a later time get some more disk space for them, you could easily overlook readjusting the value and have it bite you when you don't expect it.