Why create Test Scenarios

Test Scenarios are created for the following reasons,

Creating Test Scenarios ensures complete Test Coverage
Test Scenarios can be approved by various stakeholders like Business Analyst, Developers, Customers to ensure the Application Under Test is thoroughly tested. It ensures that the software is working for the most common use cases.
They serve as a quick tool to determine the testing work effort and accordingly create a proposal for the client or organize the workforce.
They help determine the most important end-to-end transactions or the real use of the software applications.
For studying the end-to-end functioning of the program, Test Scenario is critical.