A worksheet and a handout are divisions that can include the workspace attribute on various elements. In HTML output, you get a print preview button that then renders that workspace and creates page-breaks for printing.
But what if you are in the middle of a section and want to author a set of tasks for your readers to do, perhaps on paper? Now you can add workspace to any of the Project-like elements (project, activity, investigation, exploration). These will then also get the print preview button. Think of it as a mini inline worksheet.
Available in CLI version 2.47.