As I see it, the checkbox is selecting *[whether or not to] Show [the] sidebar*, and it's clearer than just *[checkbox] Sidebar*. OTOH, e.g. LibreOffice and GEdit don't have the *Show* part in their items, so maybe it's common/expected. Yet, I don't see anything about this in e.g. [GNOME's HIG](https://developer.gnome.org/hig/stable/).