As image copy backup is an exact copy, it consumes more space and takes more time to complete than level 0 backup since it contains empty data blocks containing no data, still why image copy backup is needed, what is the utility of image copy backup over level 0 backup?
You can have incrementally updated backup, which uses image copy as base.
Once you take image copy full backup, further incremental backups can be applied to image copy, rolling it forward to the point in time when the level 1 incremental was created.
A backup strategy based on incrementally updated backups can help minimize time required for media recovery.
http://docs.oracle.com/cd/B19306_01/backup.102/b14192/bkup004.htm ---->Incrementally Updated Backups: Rolling Forward Image Copy Backups