Big-big + 1" is a foolproof way to make sure you'll have enough chain for your setup, on the first try, as long as you don't change anything.
Like FBinNY and others, though, I like to use as much chain as I can. It gives a little more flexibility to try different chainrings or cassettes later on, or if you have a mishap on the road and need to cut out a link to continue your ride. Plus, I paid for all of those links, so why not use as many of them as I can?
