This kind of chess battle doesn't happen very often. We can compare it to Fisher-Spasski or Kasparov-Karpov.
If Carslen wins, this will be a generation change in the chess world.
Given the popularity of chess in Asia, it is estimated that about a billion of people are following this match[1].
[1] http://www.gq-magazine.co.uk/comment/articles/2013-11/14/mag...