A few of our clients have WordPress Multisite installations with quite a number of plugins. For security reasons alone, it’s never a good idea to keep unnecessary plugins on the server, even if they’re not in use. With constant changes and development going on, it’s easy to lose track of them.
Going through each site manually and checking which plugins are active can be a pain, but luckily I discovered an excellent plugin called Network Plugin Auditor, available for free on the WordPress Plugin Repository. The plugin does two things: in the Plugins list of the Network Admin, it adds an extra column, showing all the sites any specific plugin is active on. It’s then trivial to remove plugins where that last column is empty. ALso, on the Sites page the plugin will show which plugins are in use on each site.
Highly recommended for Network Admins using WordPress Multisite!