For SSDs I'm not sure. My data drives, SSDs are still too expensive so I haven't switched. Spinning rust it definitely does matter (for drive lifetime and also contention).
I've always figured that for spinning rust, what kills them is power cycles. So, unless you're absolutely sure they won't be woken up, disable "sleep" mode. If you're sure nothing's going to wake them up, might as well turn them off completely, and the server also, saving a buck or two.
