Roon is doing a lot when it’s not playing, like metadata updates that don’t touch the spinning drives. However, if it is truly idle, then it writes resource usage status periodically to the log. The fact that nothing else is logged during these stats often helps us find the cause of issues that members raise.
ROCK does not spin down drives as a choice. Spinning up and down drives decreases their longevity quite a bit, and in some circumstances can use more power.