Are Preorders Still Relevant, and Are they Really Harmful to The industry?

Its everyone;s favorite topic, preorders! With modern Day gaming, and digital gaming increasing with each year. The question is are pre-orders still relevant? Why preorder a game if you're almost a guaranteed that the game will be in stock? Is there a reason you still preorder? With Gamestop, Best Buy, Amazon, and more fighting for your dollar, and locking content away behind a 5 dollar pay wall, shouldn't every copy of the game be the same no matter where you shop?