A command-line tool should run only one copy of its nightly export at a time. A small web app wants to cap each user at 60 requests a minute. A desktop app needs to remember when it last synced. All three are state: an integer, a timestamp, an owner. All three usually get solved by adding Redis, because Redis has the verbs for them: INCR, SET NX PX, EXPIRE. The app needed the verbs and got a server along with them, a port and a persistence config included.