Adds a 'Manage dependencies' tab to the admin page for content types.
This lets you set a 'target field' whose visibility is set according to a 'control field' and whether the latter is full/empty/checked/unchecked/has a specific value.
Another useful feature is you can prefill/pre-tick etc. the target field (including with a custom text value, for example).
To detect quickly if it's in use anywhere (I needed to do this before being sure I could uninstall the module on a site), export your site config and grep the /config/sync directory for 'conditional_fields' - it's stored in the 'third_party_settings' key in core.entity_form_display.node.[content type].default.yml