I actually used to work for a company that developed tools for administrating and interpreting DISC assessments. It's actually really interesting stuff - we all tend to have some assumption at some level that other people think like us, value the same things that we do, and have the same reactions to a given situation that we do. DISC asserts otherwise - just because I want to be treated one way doesn't mean that you want to be treated that way, and by understanding those differences, we can eliminate friction in communication.

Once you can learn to read how others want to be treated and know how to modify your own interactions with them accordingly, your ability to successfully interact with a wide variety of people vastly improves. It seems obvious and handwavey, but in my experience, the vast majority of tense relationships or awkward interpersonal interactions are because of a failure of two people to understand each other. Even if they're both behaving in the way they'd want to be treated, that doesn't mean that they're treating the other person as they'd want to be treated.