Is there a way to review users' usage of self service procurement?

Summary:

Is there a report which we can run to review when users last used their access to self service procurement, in order to manage which users require access?

Content (required):

We use metric reports to review how many users have the privilege which grants access to self service procurement, and triggers use of the self service procurement license. In order to review who has this access, and remove it from users who no longer need it, we're looking for a report showing users who haven't needed their self service procurement access in, for example, the last year - does such a report exist?