Yea but you can also semi damage the brand if the movies suck.So much untapped potential still left in the HP universe. Stories that can still be told. It seems like Rowling is just now waking up to that.
Look at stuff like Star Wars and Lord of the Rings, and at how the their universes and lore have grown throughout the years through various forms of media(books, movies, games.etc).
Prequels aren't looking like a good idea after star wars and hobbit. Financially maybe but fanboys and critics weren't happy