Whilst, in the example you provide, it might be the case that "N = all", the cautionary tale offered in the article is that you always need to make sure you are

Whilst, in the example you provide, it might be the case that "N = all", the cautionary tale offered in the article is that you always need to make sure you are asking the right question, and it is pretty easy to confuse yourself. So you said "if i work for facebook and i want to figure out something about my users", and for whatever you were doing, looking at your existing user base might be the right thing to do. Perhaps, though, you actually want to know something about all your potential users, not just the users you happen to have right now. Whether or not your current user base offers a good model for your potential user base would then be a pretty important question, and one that almost certainly isn't answered by "big data". I think that, as with most of statistics, the key point is "think about your problem", and that focusing on a set of solutions rather than the problems themselves can get in the way of that.