What is a project charter good for?

A project charter issued by senior management formally authorizes the initiation of a project and gives the project manager authority to apply organizational resources to project activities and tasks. It includes a description of business needs and how the project will address those needs.
Though limited to a high-level overview in its initial form, the charter should provide sufficient detail to perform the actions or reference a separate business case that has the following:

• Shows alignment to enterprise strategy, goals and priorities
• Illustrates how the project deliverable will meet specific business requirements
• Establishes clear success criteria based on measures of client satisfaction
• Identifies funding sources and high-level costs
• Identifies qualitative benefits and translates to quantitative measures
• Establishes appropriate interval(s) for updated cost estimates
• Examines assumptions (such as system performance or skills needed)
• Identifies risks and prepares mitigations
• Factors risks against cost and benefit
• Selects the project's guiding principles and methodologies
• Communicates control mechanisms to stakeholder