Here’s a short 4-minute video by Light Club that looks at using a vertical or horizontal middle line through the frame, something it refers to as “a secret rule of photo composition.”
Examples given in the video show how both photographers and artists throughout history have created compelling compositions by placing their subjects and scenes along the middle line (e.g. portrait photographers placing one of the subject’s eyes directly on the line).
The rule of thirds proposes that placing points of interest off the middle lines helps produce tension and interest, but this video argues that “there’s magic in the middle.”