It was actually cropped on all 4 sides: https://news.artnet.com/art-world/operation-night-watch-1982...
The structure of the painting is very common: a central figure surrounded by a semi-circle of figures. For an early and clear example look at The Tribute Money by Masaccio. The crop on the left plays hell with this structure. It also moves the central figure maddeningly close to the middle. Rembrandt would never have voluntarily placed a figure in the middle of a multi-figure composition.