As this question is unanswered so far, I will try. But I think, that no definitive answer for this exists, an answer will contain some part of opinion. Also - as Joseph Wright points out - you may want to have a look at Why should I use LaTeX? and What professions use TeX/LaTeX besides CS?.
(La)TeX is great for producing texts while concentrating on the content and without too much distraction from caring about design. LaTeX can have a neat design, but the main focus is on producing text. So for essays you should be fine. Be warned, that LaTeX is not totally easy to learn, if you have to get ready an essay for tomorrow, don't try to learn LaTeX now. But if you learn it, you may save time later, because you can make all your essays with the already predefined macros and style.
You also talk about graphic design, and that may be a little more difficult. While LaTeX is able to make nice designed documents, most designers prefer to see direct output. That means, if you change something in your design-program, you see an immediate effect on the document. In LaTeX you always have to compile the document first. So, if you already have a license for a design-program and seem to able to use it, you may better use that for your design-work.
Is it worth learning LaTeX? In my opinion yes, especially if you produce many texts: reports, books, articles. What kind of people doing different subjects/occupations use it, and why? Hard to say, who uses it, but it is clear, that LaTeX seems mostly be used in science. Why? I think, everyone has another answer. For me is it the focus on the content, and doing design other days. I can even separate styling-issues in different files than the content. If I already had a solution for look for one document, I can simply copy/paste it into in similar document for same look. And as LaTeX uses simple text-files, I can use all programs for working with simple texts, from Unix command-line tools to version control.