The Design Canvas tab displays the options for the types of widgets that are displayed in the Widgets sections along the left side of the page. By default, all widget types are available. If there is a requirement to remove an option, remove its check box and publish the changes.
For example, the application may require that no users be able to create new lists and libraries within the site. In that context, remove the checkmark from the “Content” option and the entire Content section will be removed from the Widgets.