Going online/digital allows you to go big, as I discussed a few posts ago, Reaching Critical Mass Faster, but is not always about going as big as you can. Strategy trumps size, unless size is the game.
For most brands it is about reaching the right people. There are so many social communities that some times the biggest one is not necessarily the ones that will achieve the maximum results for that brand.
Even when you are working with the largest communities, they have inner circles.