What is value of Business Case in project charter?

First step of any project is to develop business case. After careful review we decide if it can be project or not.

It is the strategic dimension of the project.i.e., why we do the project?

Agreed with Wahid

Vital element for decision about project drivers

Value of Business case is like brain of human 

Business case will explain all in/out of project. It is developed by Business or PM

Business case establishes the fundamental rationale for a course of action. It is the documented history of why a project was selected. It details the objectives, the projected outcomes, and the projected investments associated with the effort. As such, it allows decision makers to examine the breadth of information currently known about the effort to determine whether or not the project is a good idea in terms of cost, benefit, and organizational objectives.

Business case is first document to start Project Charter. Without this how you know the reason of project and deliverables.