Fully utilizing the resource means some benefit is obtained, certainly. But when the cost of the resource to the user is zero, that means the benefit only need be greater than zero.

Have you ever worked on a shared compute cluster? In general, disks fill to capacity & machines run at capacity, no matter what those capacities are. It's bloat; files that don't get deleted until you run out of disk, because deleting files takes ten seconds. Massive processes that are left always-running to save ten seconds of launch time. So on and so forth. Basically, the user is getting some value. But it's very small, and thus makes a poor reason to make expensive upgrades to the cluster.