Compositions featuring characters looking back have a soft aura about them. The character can be looking back with fondness and desire or with hesitation to move forward. It also allows areas not seen in full frontal views a chance to shine, like dresses with intricate back designs.
Oberon (from Fate/Grand Order) is giving you a good look at his wings as he beckons you toward the sunset.
Some of the illustrations below are so good they may have you looking back as well.