According to dire's video, if you don't choose things like weather and sun and sky, the RNG will choose them. And things such as villages and ravines, if not chosen will be added as well. He specifically adds in 3 symbols from these area's in order to stop the RNG from trying to add more (Go to 11:01 in the linked video, again at 12:05 in going over sky color, again at 13:30). These are not "essential" for the world to be created, none of the symbols are that essential. They are essential to controlling the RNG. Check the video I linked, he restates it over and over and over again (almost every time he adds a symbol he says it) "the more accurately you write your book the less randomness there will be."
Start at 1:10 he specifically states, that they are required, either you put them in or the RNG does. It's apart of the grammar system. He goes on at length on this topic. These are required to control the RNG. "If you leave things out it's going to randomly add things in." "The grammar system automatically adds things in." "You might randomly get stone blocks, but you might get randomly chosen diamond ore, causing instability." "You might also get instability if you write your age incorrectly, or the grammer system adds a symbol that would add instability". An example of this, is the sun symbol. If you chose just normal sun, the grammar system might chose no or a few modifiers, the right number or not enough, this can cause instability in itself. At 10:30 he goes over this again. He chooses the sun, but not the stars or moon, so these will be randomly chosen and could cause problems. At 21:55ish he sets up a walk through of all the symbols he used in the age he writes in that video.