Earlier quoted context omitted.
You're always paying for power regardless of whether you're offering your unused drive space on a distributed system.
Hard drives consume less power when idle, like CPUs.
And there's the added likelihood that people providing hdd space on filecoin are not going to even measure the impact of extra power consumption, they're just going to notice the revenue. (Not that this is a good thing, if someone was losing money, they should know)