One thing I have noticed with working with multiple people across multiple projects, is that some tasks get scheduled, and abandoned or scheduled and the project is archived (so the task still shows). Only admins of a project can change some settings, so if that user is not available, it cannot be corrected. For projects, that are archived, it does not show in the interface, who the owner is.
A superuser would be a good idea to allow them to prune any projects causing clutter, so they could effectively be admin of any project to correct errors from other users and manage the whole instance.