Well actually it depends on if the temp tbs is created as temporary or permanent. If temporary it never deallocates temp segments(unless you restart the database), if permanent SMON cleans temp segments. Temporary is to prefer because the database doesn´t have the overhead of deallocating extents all the time. The worst situation i have seen is a 30 GB temp tbs created as permanent and with the next_extent size set to default 30(?) Kb. It took oracle 4 days to deallocate the extents and under this time no temporay segments could be allocated EVEN when we created a new temp tbs!!!

/Tuve