Indeed. One actually useful case I found was using an rpi with shairport-sync + owntone to allow airplay streaming. I got a quality DAC from hifiberry [0].
Another use was running HomeAssistant, but I migrated that to my real server.
Another use is having an external InfluxDB + Grafana monitoring setup so I can view stats even if the server goes down.
Lastly, you can take X amount of raspberry pis and run a kubernetes cluster with k3s. [1]
Since I don't play with my cluster much, most of my pis just sit around gathering dust...