There has been lots of discussion over the internet about one major advantage in nWoD. When you buy World of Darkness core rule book, you basically buy rules set only once. After it you decide by buying the supplement you want to run or play. You don't have to buy basic rules over and over again with every new book. Also, the rules are the same for every "race" was it Vampires, Werewolves, Mages, Changelings, Hunters etc. In those supplement books come ofcourse additional rules for those "races" but core books are always the same. Always the one you originally bought in that one - World of Darkness - book.
But, even if that explained upper is a great advantage, there is also a minor disadvantage. You always have to have (atleast) two books in hand. For example, if running Werewolf: the Forsaken book you need to have World of Darkness book for general game rules and also W:tF book for Werewolf special rules (and setting).
As played today Werewolf: the Forsaken, I noticed that I have to check two separate books to figure out how things work. That was kind of a annoyance. It reminds me a bit of Dungeons & Dragons where you got own book for GM, other for players, third for monsters and possibly fourth for setting. And few extra books for advanced rules and other supplements.
Before, when I played Vampire: the Masquerade and Vampire: the Dark Ages it was quite simple. I basically just needed one book to run the game. Still, even if I had to buy rules several times with every new book, all I needed was within one cover.
Conclusion for nWoD is not absolute. It is good thing that you only buy one time the rules and the space used in next books is not repeated over and over again, but yet you need several books in hand to run the game.