With RMAN configure controlfile autobackup set to ON, RMAN automatically creates a control file and an SPFILE backup after you run the BACKUP or COPY commands. If you have a daily backup task, you will see autobackup of control file and spfile created every day after your main backup. That is good, huh! They are supposed to be managed by the retention policy and deleted automatically when become obsolete. However, possibily due to bugs:

• Bug 25943271 : RMAN REPORT OBSOLETE DOES NOT REPORT CONTROLFILE BACKUP AS OBSOLETE
• Bug 26771767 : SPFILE BACKUP OR BACKUP PIECE INCLUDES SPFILE ARE NOT REPORTED AS OBSOLETE

They won’t be marked as obsolete when RMAN retention policy is configured as redundancy. For example:

CONFIGURE RETENTION POLICY TO REDUNDANCY 1;

To work around this, change the rentention policy to recovery window and do a crosscheck on backup.

CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 8 DAYS;

crosscheck backup;

delete obsolete;

Or delete autobackup explicitly after certain days.

• Oracle