Captain, I think you hit the nail on the head; you don't need, but there are people that use them (A,B &C). It is a like thing; I like blue you like red, each are colours (colors). Personal preference. I have a skimmer that I used with my new tank and I used it with the cycling process, I mainly did to practice my maintenance routine. As for my sump it came with my new tank, it just gives me extra water volume.
My 1st tank did not have a sump or a protein skimmer and my fish are very happy. Enjoy what you have, I would also suggest more LR
, it looks good and helps with the filtration!