I just had this conversation at work. It reinforces a very import user behavior that a few years back everyone messed up. We used to think you had to fit everything "above the fold". After running a lot of multivariate tests, watching user behavior and using websites, I learned that the fold, in most cases, is myth.

It turns out that people will scroll down, if there is a compelling reason to. Now, having elements partially off screen is a very simple way of ensuring people will continue to scroll down. And in the last few years, with the proliferation of the infinity scroll, off the screen elements are more popular than ever.