At a bare minimum, it will give you a fresh perspective on things you already knew. In my experiences, there will be things you didn't realize about yourself.
They aren't going to tell you what the solution is to all your problems; that's for you and your doctor to figure out. They will give you everything you need to make well-informed decisions, and that's priceless.
Regardless of whether the conclusion is "yes you have x" or "no you don't have x" the diagnosis will be accompanied by a detailed analysis of your psychological condition. Whether or not you are diagnosed, that analysis will cover the issues that led you to believe you may have that condition.