It's crazy how scripts are on lock down. QT films and Deadpool prove it doesn't affect box office. It's reading Harry Potter books before watching the films. One could argue, especially in my case, reading scripts makes me want to see a movie more!
Deadpool was leaked by the writers on purpose, so not a great example. I think the bigger fear is negative buzz -- like with Aloha, well ahead of release, due to the Sony hack. If a script is still under development and gets out there, it could slow development process.