Diagonal lines are one of the influential elements in an image and can create a point of interest. Apart from that, it can also provide depth to the image through perspective.
Some photo references:
quacK! by priskoskis
Damnoen Saduak by Kaptah
Row by historygradguy
4:3:1 by Jimmy su
Untitled by piriskoskis
Kayaks for rent by drurydrama
Reading by Stephen Gray
\ by Antonio
Ferocious killer by Thomas van Rooij
Connections by weltreisender2000