>This tells me what it is, but now where it's used for...

The manuals don't come out and say what the GUID is for, but one can
see its purpose...  These days, many hosts respond on multiple IP addresses
and network names (Virtual IPs).  Discerning the actual identity of the
connecting system becomes problematic.  Assigning a unique ID within an
application allows ready identification.

  Richard Sims, BU