There are often different reasons for why people do a DM course.
I was very happy being a Rescue Diver and I took it very seriously. Maybe just because of the way I am I was always helping other divers to kit up/ kit off in the boat, keeping an eye on people other than my buddy as well and so on. I would also put in an extra effort with loading, unloading, cleaning up and so on. I like to meet new people and open up conversation. So frequently in places I was diving where the Instructor knew me he would say "And Leapfrog is going to go behind the group to keep an eye on things". After a dive, I would often get comments like, "How did you become a DM?" "Or thanks for helping, it's so good to have a DM like you around". Well that of course made me very pleased with myself. Eventually one of my mentors, a PADI Master Instructor said:" Look, you better do the DM Course because everyone already thinks you are one and one day it could mean trouble if something goes wrong". So I did the course and suddenly I found myself as a role model to the non professional divers but at the bottom of the PRO ladder, so it was also a humbling experience. It was by taking this step that I realized that I wanted to be an Instructor (full time). Suddenly, I looked at my life and decided to do what I wanted to do and not what others thought I should be doing. So I went to work for a LDS and I got involved in everything including managing the biz, operations, sales, DMing, the works..... most of the people I had to coordinate were OWSI, MSDTs, Captains and so on, so I had to do all of this humble as pie (that was a good experience in itself). I also got a chance to teach under direct supervision mainly OWD and Nitrox courses. Recently I did my IDC, my IE and here I am, starting life as a freelance instructor.
The theory you will learn as a DM will make you a better informed diver (not a bad thing).
The practice you get by actually being a DM should make you a better diver.
Who knows, you may find out you want to be a teacher...............God help you!