I kept reading and kind of answered my own question, but I will post incase somebody searches.
First off, fuel consumption seems to be around a gallon an hour at high idle, although highly debated. That does seem high, I know CAT motored Pete 379s I have driven use about half a gal an hour and my deuce uses about a 1/3 a gal an hour idling. The best thread on this subject: How much fuel do I use idling? - Ford Truck Enthusiasts Forums
Second it seems that in the Ford manual it states the following:
Page 14 of the 6.0L Diesel Manual:
The following cold weather idling guidelines must be followed:
• Avoid idling the engine for more than 10 minutes at a time.
• Use Motor Craft Cetane Index improvers of a non-alcohol based from a reputable manufacturer.
• Maintain the engine cooling system properly.
• Do not shut the engine down after an extensive idling period (10 minutes or more). Drive the vehicle for several miles with the engine at normal operating temperatures under a moderate load to burn off any accumulated carbon and varnish.
• Consider using an engine block heater.
• For extended idle times use an approved idle speed increase device.
That last line ^ pretty much says to use high idle and answers my question. I assume it is mainly for the EGR valve, but also for preventing wetstacking the turbo.