As you work with MakeCode you may eventually have many projects saved in your browser's local storage. These projects also appear as cards on the home screen for you to access again and continue to work with them. At some point, you might decide that there are too many projects for you to manage or that you are no longer interested having those projects available to you on your local computer.
You can remove your local projects using the Reset option in the Settings menu. This will clear all of your projects from the browser's local storage and remove them from the home screen.
Go read the page about saving projects to see what gets kept when you save a project.