Following good project management practices, we have set a baseline.

Following good project management practices, we have set a baseline. How is a project baseline used to guide the execution of the project's work, to evaluate progress and performance, and to control the project? Also, as you continue to think about monitoring and controlling the project, specifically consider the question: How can the project baseline and the earned value approach for variance analysis be used to monitor and report project progress?

*please answer the WHY question. a short paragraph is fine*