There are lots of things you SHOULD NOT do with your NAS. While the legal ramifications of what you do with your hardware may cause you legal problems, that isn't something we plan to address. You shouldn't be doing illegal things. That said, here we go.

It is not recommended to spin down drives that are pools or part of pools in ZFS. Periodically, drives that are part of pools that get spun down don't spin up gracefully later, and this will make the pool (in some cases) unusable, forcing you to reboot to get the pool and system running right again. So, please don't spin down ZFS pool drives. (also it wears out the hard drives faster while saving you some minor power usage)

This is most notable with rotational drives that are attached by SATA to USB adapters, and the drive is inactive long enough to be spun down by the toaster/adapter. So, using ZFS with drives attached this way is definitely not recommended.