During media recovery, RMAN examines the restored files to determine whether it can recover them with an incremental backup. If it has a choice, then RMAN always chooses incremental backups over archived redo logs because applying changes at a block level is faster than applying redo.
RMAN does not need to restore a base incremental backup of a datafile to apply incremental backups to the datafile during recovery. For example, you can restore datafile image copies and recover them with incremental backups.
http://docs.oracle.com/cd/B28359_01/backup.111/b28270/rcmcncpt.htm#BRADV89497