In my corner of the world, I do not think I have ever seen harnesses in use just to be up on a roof. I've been up there many times myself, either cleaning clogged gutters or putting up Christmas decorations. Unless you have a very steep roof, and here they would build up scaffolding for that, or are not wearing sensible shoes/boots, it is not really very dangerous in my opinion. It is much riskier getting off/on the ladder to get up there.
Here at least asphalt shingles are by far the most common, and such work is difficult in the weather, messy and hard on clothing, and can be quite smelly. I talked with the owner of the company that put my original shingles on. He would not let his kids work for his company. While he appreciated that he had done well, he did not want to subject them to a lifetime of dealing with it all. I only did my own roof once many years ago, yet totally understand what he was saying.