I've been using it for years. It's important, because a lot of people think that the airplane determines the seating configuration. Not at all. Depending on the airline, a 737, for example, can have very different amounts of legroom, the rows can be numbered differently, etc.
It's like a Boeing marketing guy said to me once, "We just sell a tube that flies. When people buy one we say, 'You want seats with that?'"