diskutil can be used for many tasks related to the hard drives, optical discs and RAID sets, here are some of the tasks I use it for

diskutil info /

provides information on the selected drive, my example would get info on the system drive

sudo diskutil repairPermissions /

would run a permissions repair on the system drive

diskutil listFilesystems

Shows the file system personalities available for formatting when erasing and partitioning a disk

sudo diskutil umount /Volumes/SELECTED_VOLUME

running this will force eject the volume specified, to see the list of volumes available type ls -la /Volumes/

sudo diskutil verifyVolume /

verifies the data structure of a volume

for a full list of tasks you can do with diskutil type man diskutil