There are some indications that higher alk levels can increase the speed that coral can produce new skeleton thus increasing the growth rate. There are potential problems with keeping it that high though, such as an increase in the rate of abiotic precipitation (precipitate forming on heaters/powerheads etc), you also may run into issues with your alk at a higher level if you also use kalkwasser, you may have trouble keeping your pH low enough. There is less margin for error at the higher levels, if you get a spike in alk levels you can get a "snowstorm" where calcium carbonate precipitates out suddenly as it hits the breaking point which can cause large swings in alk/calcium as it precipitates out. Keeping it on the low end is not necessarily a bad thing though, for one thing, depending on your pH you can see a much better growth rate than you would expect for the alk level. http://www.3reef.com/forums/water-chemistry/low-ph-may-not-end-world-75962.html Also for people running ultra low nutrient systems (bacteria driven like prodibio/zeovit/vodka/carbon dosing) lower alk levels are generally recommended otherwise some people see negative effects on their coral like "burned" tips on acros. I think some people just go with lower levels because it's easier to maintain based on what their salt mix starts out at as well. Just some of my thoughts on the matter.