FWIW, On a modern build, the power-savings by letting drives sleep is pretty minimal.
Let's say you have a HD in a USB docking station.
Most of those have firmware that automatically puts a drive to sleep after several minutes of inactivity.
Unfortunately, you don't have access to change this sleep function/behavior.
When going to save a project, the machine will spin-up that HD (waiting for it before completing the action).
I'm impatient... and that drives me crazy.
Another example, let's say you allow your "Samples" drive to go to sleep.
On one particular project, you're not using any disk-streaming samples until the bridge of the song.
When the bridge hits, you're playing a really busy part with lots of sustain pedal (lots of disk-streaming polyphony).
By the time the Samples drive spins back up, it's missed the beginning of the bridge.
This is also an example of why any type of performance throttling (for DAW purposes) is not a good idea.
Machines are great, but they can't reason.
During the bridge, the song breaks down to kick and lead vocal... so the OS/motherboard decide to significantly reduce clock-speed and park CPU cores.
Right after the bridge, the song has a massive chorus-out... with 24 tracks of backing vocals, stacked synth tracks, full string section, everything but the kitchen-sink.
That's going to result in a transport drop-out.
With performance-throttling fully disabled, this is never a concern.