Self-knowledge yields independence of mind
When you understand how your emotions affect who you are, it becomes much more difficult for someone to manipulate you into something you don’t want or need.
When you can trust yourself to make the best decision for yourself, you can relieve a world of anxiety when making decisions.
You are the expert of your own being. You are in charge of your thoughts and you are your own personality.
Understanding your own needs and what you want out of a romantic/partner relationship yields happiness and fulfillment (or at the very least avoiding constant misery).