This tip or strategy is actually more a philosophy or strategic attitude about business relationships. The message is one of abundance. Share your contacts, be free with suggesting and assisting new relationships, and make a focused effort to introduce your contacts to others.
Don't adopt the attitude or behavior that suggests you want to keep your contacts (clients, customers, prospects, and friends) to yourself. If you have a protective, excluding attitude, neither you nor your business will be attractive to new people - others might very well come to see you and your company, or at least your part of it as a closed group, or at least not a welcoming group, and look elsewhere.
One of the largest networking organizations, BNI (Business Networking International) has the slogan, "Givers gain." BNI succeeds because of its structured networking organization where chapters meet weekly and there can be only one representative per industry - while on the surface that policy may seem exclusive, in reality there are many opportunities within BNI to develop relationships outside the group and the welcoming, open atmosphere and attitude of most chapters demonstrates the members' practice of the organization's credo.
I'm not suggesting you refer all your clients to direct competitors and give away your business, but I do firmly believe that as you are open to make, develop, and share relationships with an ever-expanding circle of contacts, it benefits everyone, most especially you!