John Hess From FilmMakerIQ.com traces the evolution of the screen shape from the silent film days through the widescreen explosion of the 50s, to the aspect ratio of modern digital cameras. If you've ever wondered why and how the formats we use today came to be, this is something you'll want to watch. The topic is too broad to summarize for those that would prefer to not watch his video but, there is one piece that definitely stuck out to me.
At the end Hess closes with this: "It's still only a shape. A canvas on which to draw your story. The canvas does matter. How you draw it makes all the difference, so use aspect ratio...and make something great."
The point to me is not to let yourself become confined to one format, but rather to let yourself experiment and find the right frame to create your image within.