What is the difference between DELETE INPUT and DELETE ALL INPUT in RMAN?

With DELETE INPUT, RMAN only deletes the specific copy of the archived redo log chosen for the backup set.
With DELETE ALL INPUT, RMAN will delete each backed-up archived redo log file from all log archiving destinations.

For example, assume that you archive to /arc_dest1, /arc_dest2, and /arc_dest3, and you run the following command:

BACKUP DEVICE TYPE sbt 
  ARCHIVELOG ALL 
  DELETE ALL INPUT;

In this case RMAN backs up only one copy of each log sequence number in these directories, and then deletes all copies of any
log that it backed up from the (potentially multiple) archiving destinations.

If you had specified DELETE INPUT rather than DELETE ALL INPUT, then RMAN would only delete the specific archived redo log files
that it backed up (for example, it would delete the archived redo log files in /arc_dest1 if those were the files
used as the source of the backup, but it would leave the contents of the /arc_dest2 and /arc_dest3 intact).