Even though they call it a "mood" disorder, I think really that's a misnomer. Like, what is happening to you may effect your "mood" but really there is a lot going on that effects your functioning.

I agree with Newtus that it's important to know little details. For example, you may have bipolar but do you have psychotic features or not? Do you have more lows or highs? Are you rapid cycling or not? There's a lot to it and the more you know about how it works for you specifically gives you more tools on how to work towards wellness. It's like GI Joe used to tell us every Saturday Morning "The more you know!"

Some things may be for insurance but other things help because if one doctor looks at your dx and then passes it to the next, it gives them clues into what to expect. That's the whoel point of language, so we can understand ourselves and each other.