More Q's About Publishing: Movie/TV Adaptations?

I've been wondering about this since we wrote down publishing questions in class. When I was little in my fourth grade class, we had written small novels and also small author biographies. I remember writing in mine that my dream was to write a book and then have it turned into a movie. Back then, I didn't know what that entailed and now, I'm still just as clueless.

Does this change anything in terms of the publishing industry, or does it just move the whole project over to the movie industry? I imagine there must be some intersection, and what happens if the author wants to contribute to the screenplay or help with production?

With all the movies out based off books, it begs the question. The most obvious example would be the Harry Potter series and their immense success as novels and films. Another example is John Green, who has had a couple of books turned into movies and then Looking for Alaska was adapted into a Hulu series. I haven't seen Looking for Alaska  the series, but Fault in Our Stars and Paper Towns were not super memorable or groundbreaking.

Of course, for publishing houses, this could be a good thing. If a movie adaptation gains popularity, naturally more and more people will want to buy and read the book. (You know that saying where the original book is usually better than the movie, and it usually rings true.) This could lead to more prints and then overall more fame and success for the author. 

This also got me thinking about how I consume books and movies, and if there are movie adaptations, which one I consume first. Usually, I'm a die-hard believer in reading the book before seeing the movie, but in recent years, my reading has dropped off quite a bit. Some movie adaptations I've seen before the book are Stephen King's It as well as "Stand by Me," which is an adaptation of The Body.  Some other favorites of mine are "Big Little Lies" and "Gone Girl."

Part of me is worried that I'll never get to reading these novels which have created shows and movies that I love so much. But if I hadn't seen them on the screen first, I might not have known about the novels at all.