The purpose of the adjustment "File I/O - Block I/O"

Hi All.
The purpose of the adjustment "File I/O - Block I/O" in new iSCSI volume action, on CONFIGURATION\volume manager\Vol. groups? After all, it is iSCSI block access.

http://kb.open-e.com/File-IO-Or-Block-IO_342.html

Thanks for answer.
And how does this apply to Microsoft initiator?
He reacts the same way as the target a creature with a "File I/O", and the target created with "Block I/O" - see it as the logical volume.