I've seen so many different thoughts on reef temps that it's hard to decide
Lower temps, as Brad stated, allow for more oxygenated water
Most infections will spread / progress slower @ lower temps due to metabolism
Metabolic rates of corals are slower @ lower temps, and sometimes that's not ideal
Some will set their target temps based on their home room temp, and even so much as the time of year
Some of this habit is an attempt to use less electricity
Here's some opinions and reading for you;
Keep in mind that I think some who responded to the canreef poll were a bit off with their conception of Celcius to Fahrenheit conversions as 26c is 78.8ish and 27c is 80.6ish
http://www.canreef.com/vbulletin/sho...ight=reef+temp
http://www.reefcentral.com/forums/sh....php?t=1869167
http://www.ronshimek.com/salinity_temperature.html