You don't. As Flots Am stated; they're there to get you to pay a little more on a dive. They're main use is in assisting instructors during training, and to provide a level of professional certification for mates that is below an instructor.
When they're leading, they also induce complacency and a distinct lack of awareness on the part of divers, even good experienced divers. Divers become sheep, following the Border Collie around the field, relying on the DM to keep them safe, when it should be themselves doing this.
I've watched instructors, other DMs and good divers on vacation swim hard to keep up with the DM, passing by uncounted cool stuff because they felt like they had to stay with them.