Diagonal lines are good. Horizontal and to a lesser extent vertical lines are bad by comparison. By this we mean that in photography, diagonal lines draw the viewer’s attention into the image creating a dynamic and tension element into an otherwise staid photograph.
This is why photos lacking diagonal lines do not move our subconscious to the same degree and are, in effect, boring by comparison. Take a look at the lead photo here: “Refugees: Rebuilding After Typhoon Mary“; Hong Kong (June 15, 1960). The toddler in the left foreground is a plus, but see how many vertical lines you can find in this photo. In the background is Victoria Peak. See: Typhoon Mary.