There are lots of rules in photography, like don’t have your horizon in the centre of the frame, don’t have converging verticals and use a telephoto, not a wide angle lens for portraits. All good advice and worth keeping in mind most of the time.
On the other hand; sometimes you can get fantastic results from bending or breaking the rules. Take the above photo. Mark is a fantastic piano player who comes across as a very serious guy when you first meet him. But under the serious exterior, he has a terrific sense of humour. A medium telephoto lens, say 80mm or 105mm would have been fine for this backstage shot, but the 10mm f2.8 fisheye really helps to show you that Mark isn’t so serious after all. If a rule’s worth breaking, it’s worth breaking to the extreme.