What is the role of a mission statement in planning?

"An organization’s mission is formalized in its mission statement, a document that states the purpose of the organization and its reason for existing. For example, Twitter’s mission statement formalizes both concepts while staying within its self-imposed character limit. Twitter’s mission is to give everyone the power to create and share ideas and information instantly, without barriers. Its values state that the company believes in free expression and thinks every voice has the power to impact the world. Its strategy is to reach the largest daily audience in the world by connecting everyone to their world via its information sharing and distribution platform products and be one of the top revenue generating Internet companies in the world. Twitter combines its mission and values to bring together a diverse workforce worldwide to fulfill its strategy. The three parts of a company mission statement are purpose, value, and action. In all organizations, plans and goals at the tactical and operational levels should clearly support the organization’s mission statement."