The only golden rule that i follow, "writing is rewriting" and "Know where you are going." Though, knowing the ending basically equals this.
To answer your first question. Yes, i have an ending for every one of my stories. I know what voice i have, and what message i want to tell the audience. The key is to not preach, but show through the story how i want to change the world. I hold on to the belief that writers are teachers, philosophers, and innovators.
The end is the most important part of any story. It tells the audience what purpose your story serves. How everything you have written cumulates into something significant. Anyone can write the beginning of a story, harder to write the middle, impossible to write the end. What do i mean by that? A good ending is always hard. It connects everything. If your story just ends, without purpose, it means you sucked as an author. If you know the ending, you have a finish line. Try to understand that.
I know a lot of people say, i want my characters to be "free" or i want my world to be "limitless." That's all good for the beginning stages of writing your story. However, as i have seen, you end up 1-5 years later, and you still haven't written, formed, or even thought up a good story line, with an intriguing enough premise, with any well formed structure. The problem here is they kept thinking up a new beginning, or moved on to other characters. Even worse, you spend months/years, on a written piece and realize you have to scrap it because (1) editors tell you to do so, (2) you realize that nothing in it matters to the story, (3) it is completely different from the rest of the story because you kept changing your mind.
You can find it in youtube with creatives (authors, screenwriters, etc.) telling you their experience, 99% do not write out of the blue, perfect the first time, with no ending in mind. Outlines serve as a guide to push them in the right direction. If you don't complete the story, by having a beginning, middle, and end, you will never have a rough draft. With that rough draft you can fix, tweak or whatever. Books and movies go through dozens of drafts. BUt the important part is that they are fixing a problem that is fixable. Not rewriting an entire story all over again, because you though of something completely different from your original idea.