I live in Santa Fe, NM where the elevation is about 6000 ft and I have a SXRD. Well I forgot to set the cooling mode to "high" instead of normal and about 2.5 months after I bought the TV, the cooling fan stopped working. I'm sure it had something to do with the less water molecules in the air at the higher elevation to cool my TV and I just overheated the cooling system over time.
If you live in high altitudes, definitely set the mode to "high" or you will have to go through the headache of exchanging your TV...
As for low elevations near sea level you can probably would keep it at normal but after my experience the fan in mine will always be on high.
On the newer Sony's they have a feature that is supposed to be used for high altitudes. Basically it either runs the cooling fan faster, longer, or both. QUESTION: Why wouldn't I want to use this feature even though I live in Florida? Seems to be simple common sense, if the fan is set to cool more efficiently the equipment is better protected. Is there any reason NOT to run the fan longer?