We wrote previously about Xavier Dolan utilizing a square 1:1 aspect ratio for Mommy, but a number of other examples are explored in this terrific video from De Filmkrant:

Aspect ratios have a long strange history as far as filmmaking is concerned, something that photography, another visual medium, hasn't had as much trouble with. While you may find some of these examples distracting in the context of watching the actual films, the one thing they all share in common is an attempt to expand beyond the confines of arbitrary standards to better suit the narrative.

Considering how important composition is to a film, it's still kind of amazing how easily it can be disregarded on cable networks who would rather fill a 16:9 screen than show a movie as it was originally intended. An exciting development we've seen with the internet is that even though most screens are 16:9 (or 16:10), and most video players online are 16:9, we can choose to fill that box any way we desire. This is especially important if we're using anamorphic adapters not necessarily designed for the aspect ratio of the sensor we're shooting with, but don't want to crop to something more standard.

The biggest takeaway here is that we shouldn't be afraid to push the boundaries of what is typically done as long as it serves a purpose within our story and strives to change the way it makes our audience feel about what is being composed inside the frame. 

Source: De Filmkrant