Let's say you have a system running some sort of RAID such that the remaining, online disks are all critical (meaning if any additional disks fail, you lose all your data). I can imagine a scenario where the system has some way of predicting whether one of the remaining disks are close to failure. If the system believes that one of the disks is close to failing, then I could see if refusing to perform some very I/O intensive task until the system health is restored (allowing for a manual-override, of course).