Anyone reading this:
Although skimmers can remove some good things, these are usually minor and easily replenished with regular water changes using high quality salt. The bad stuff they remove is more than worth the insignificant amount of good things remove. They remove different things than a refugium or scrubber will.
Although they are arguably not essential to any tank, they are beneficial. IME they allow for a more stable tank. I recommend that anyone, especially people just starting out in this hobby, use one. Any skimmer is better than no skimmer. There are reefkeeping methods that do not utilize skimmers at all, and they do work very well for some people. But most people in the hobby are using what I would call a semi-natural method, meaning that most of the filtration is the live rock itself, the rest coming from a skimmer and a fuge. With skimmers designed for small tanks (under around 30 gallons) the skimmer just isn't very effective. In these cases I recommend either A-no skimmer, water changes becoming more vital or if the tank isn't too small B-an over-sized skimmer (like something rated for 50 gallons). These would be small HOB
skimmers, even a Seaclone is better than nothing.
Everyone has different methods. Some people keep trying every new product and method that comes out, others find something that they can get to work well enough and stick with it no matter what. Most people fall somewhere in the middle. I prefer to stick with what is tried and true (like methods that 90%+ of aquarists use), but still keep an eye out for that thing that people are just not buying into yet because they have been trained to think a certain way. Maybe I am missing something like that here, but without better examples to truly illustrate the benefits of one method or another, I will be sticking with skimmers.