First all, my apologies if this is a dumb question, but I'm new to the brewing world... Anyway, I brewed an Imperial Stout Extract Kit and am ready to rack to my secondary fermenter. The directions say that I should add a packet of champagne yeast to my secondary. Will this affect flavor? Is this simply done for carbonation purposes? Should I be doing this for all of my high gravity brews? ie O.G. > 1.070? Also, I saw some people mention US-05 dried yeast in place of champagne yeast. What different effect will this have?