Having referrals is your most important and best way to find new clients (and retain your usual ones). You can be great at what you do, but don't get enough high-quality referrals to spread the word around about how great is your work and finding new clients will become 10 times more difficult. Instead of each time having to go around to introduce yourself to companies that usually are not really particularly interested if you have someone that already has their trust recommend you the difference is night and day. To be able to do that, of course, you need to be on top of your game. A client is not going to gamble their trustworthiness and years of relationship building to recommend a bad partner, they need to know themselves beforehand that you are someone they can trust and that gets it done.
Good clients tend to work with other equally good companies. If you can form a network in a positive area you will reap the rewards for years to come. Usually, the quality of the referrals are of the same as the quality of the referree itself. Keep your good clients happy and close so that you can afford one day to let go of the lesser good ones without too many regrets.