The main purpose is to achieve a profitable impression... in every impression the satoshis you gain from ads to be bigger than claim. Then you don't care about how many visitors they come, of course the more they come the bigger is profit. Then you want loyal members. But to have profitable impression, you have to be in good ad networks and that depends on your Alexa rank (mostly as I have seen) and then the script you use to be unique, customised. So in the beginning, it depends how much you can afford to lose, until you come to that position...