How useful are Star Wars novelizations in canon debates?

Curious to know because while the new canon reboot did leave the novels tied to the films intact (at least according to a press conference, don't know if it's even reliable anymore), there is a lot of contradictions between them and what is canon. The A New Hope novel is considered Legends by the Star Wars wiki, The Revenge of the Sith novel makes many references to work from Legends like Star Wars: Clone Wars and various EU novels, and there's lots of outdated information in the novels (such as Ben Kenobi's tiering system) as well as scenes not in the films at all.

Far as I recall the novels only matter where the old EU is concerned. They have no bearing on current matters.

So overhyped, as are guidebooks for Star Wars.

Apparently, because an author said a thing about Darth Maul in a kids coloring book, he is completely different than what happened on-screen.

The old movie novelizations don't matter to the current Canon. They re-released new OT movie novels for the Current Canon. So the old OT novels are useless.

Interesting. What about the Revenge of the Sith novel refrencing Legends or moments in the prequel novels that aren't in the films?

@gangorca: That doesn't matter either, in short none of the movie novelizations matter to the New Canon, just to the Old.

The old ones? Useless. Non-canon, according to the Lucasfilm Storygroup.