Every 90 days is a good rhythm. Subscriptions creep up quietly, and a quarterly audit catches unused tools before they've cost you months of wasted spend.
Any two tools solving the same core job, like two video editors or two scheduling apps. Overlap usually means you're paying twice for one function.
Most subscription tools can be reactivated any time, so cancelling an unused tool rarely causes real risk. The bigger risk is paying monthly for something sitting unused.