physiological issues such as difficulty in bending a knee may influence whether someone wants or needs to sit on a particular side of the plane

time of day and general direction of flight, combined with sun position, can influence where someone chooses to sit (sunny side is often warmer, and lighting/glare can be an issue for laptops and e-readers)

underseat storage space and access can vary depending on whether the row in front of you has 1, 2, or 3 seats

there are probably a bunch of other factors ...