The only reason to turn Turbo Boost off is to lower temperatures. The power vs frequency plot is not linear. As the CPU runs at higher frequencies, the power consumption (and heat production) increases disproportionately. So if, say, you want your laptop to run cooler and the battery to last longer, turning off Turbo Boost may help.
On a desktop though, and especially a K processor (which people buy specifically so they can overclock), there's really no reason to turn it off.