With all respect to the previous answerer, he failed to address some of the major benefits of a project charter (and why it's a necessary, and why there IS a point to it):
1. A signed project charter authorizes the project. A project cannot and should not be undertaken without an approved project charter.
2. A project charter is an excellent answer to this question "Hey, what was the main reason behind this project?". Stakeholders may forget with time, and the project charter is the only (formal) reminder.
3. It's an excellent high level brief about the project that rarely changes during the course of the project. Since executed projects experience a lot of changes, many of the project documents (substantially) change during the course of the project. Since the project charter is (usually) consistent throughout the project, it always is a great reference about the project.
4. How can you sell your project to the stakeholders (including the client) if you're not telling them what the project does, how much it costs, who will do it, what are the risks and constraints, and, last but not least, what will be the potential return? All these things are mentioned in the project charter.
The project charter is not optional, it is necessary.