A contract is a legally binding instrument which guarantees the benefits, unlike a company handbook which does not. This gives you stability. When you have Local 1-M for a union, you are guaranteed that management must meet you and your representatives at the bargaining table. This is the law. You and the negotiating committee that you elect will go to the bargaining table with the resources of GCIU Local 1-M, such as an experienced negotiator and legal counsel.
Collective bargaining is effective.