Currently the Miscellaneous Page Options metabox only contains the option to set a custom breadcrumb label. Entering a custom breadcrumb label will overwrite the page title in the breadcrumbs section. For sites that have several breadcrumbs, this is useful for pages that contain a large page title to help save space.
To open the Miscellaneous Page Options metabox, click on the white title bar and the box will expand to display all available options.
Over time, this metabox will contain other options as new features are added to WordPress.