It should never be used.  It's an historical option (as the
manual notes), used to un-mount the "Syquest" external drive.  This
unfortunately causes the first hard disk to RECAL if you don't have
the second disk upgrade.  With the second disk upgrade it improperly
un-mounts all the filesystems, apparently not handling the /etc/mnttab
file correctly for all the partitions on the second disk.

	In many people's opinions, it's much safer to use multiple
/etc/umount commands to unmount multiple partitions.  This works for
all cases, and there is no second guessing on what the command is
actually doing.  If you want to mimic the operation of dismount, you
can easily issue the "sync" command before the "umount" command.  As
far as clearing the "pulled-flag" as the manual indicates, many have
never had any problem just using the /etc/umount command (on floppies
as well as my other partitions and hard disk)