I thought the 4:3 aspect ratio was setting us up for some foul shyt to pop off. The narrow aspect ratio focus your attention and helps to draw you in. And I was on the lookout. It didn't turn out that way. I think it was used to symbolize Earn and Van's intimacy.
When looking at a map of the United States, obviously, we have LA on the west coast and Atlanta on the east coast. Earn wants to go to LA and Van wants to stay in Atlanta. Those are two geographical extremes and are represented by the vertical black bars on the left and right edges of the tv screen.
Earn and Van want each other. The extremes mean nothing without being a family. They'll just be blank spaces. Hence the black bars on the screen. The family, Earn, Van and Lottie, is in the middle of the screen and takes up the most space when they're together. I would have expanded to fullscreen at the end to signify that their family was whole.