Knowing your purpose simplifies your life.
It concentrates your effort and energy on what's important. You become effective by being selective. It's human nature to get distracted by minor issues. We play trivial pursuit with our lives. Henry David Thoreau observed that people live lives of "quite desperation", but today a better description is "aimless distraction". Many people are like gyroscopes, spinning around at a frantic space but never going anywhere.
Without a clear purpose, you will keep changing direction, job, relationship- hoping each change will settle confusion or fill the emptiness in your heart. You think, maybe this time it will be different,but it doesn't solve your real problem.
The power of focusing can be seen in light. Diffused light has little power or impact, but you can concentrate it's energy by focussing it. With a magnifying glass the rays of the sun can be focused to set grass or paper on fire. When light is focsed even more as a lesser beam, it can cut through steel. There is nothing as potent as a focused life, one lived on purpose.
If you wan your life to have impact, focus it! Stop dabbling. Stop trying to do it all. Do less. Prune away even good activities and do only that which matters most. Never confuse activity productivity. You can be busy without a purpose, but what's the point?