I add mine on bottling day with the priming sugar. That way I can figure out if I want to add a little or a lot. If you add it in the boil before fermentation, you don't know where your final gravity is going to be at, so why would you want to guess. That's my humble opinion. After you brew the same recipe a few times, you might get a feel for how much you like. But you can safely add on bottling/kegging day without risk of overcarbonation or off-flavors, so why not.