Change management (or integrated change control) ensures that the project delivers what was agreed upon during the planning process. The scope is evaluated against the requirements to identify any deviation. If the scope has been affected, a change management process should be invoked.

What is the need for changes in the management process to propose and review changes to project scope and budget.How does the presence or absence of a change control of change management process impact the project?

Here change management refers to integrated change control, and not to organizational change management (the people side of change).

Refer to A Guide to the Project Management Body of Knowledge: Chapter 4.6 Perform Integrated Change Control for details on how to handle change on projects.