What does this exactly do?

[Agera One]

Does turning off "hard disk means" shutting down the power to the drive? That would mean a SHUT DOWN. So
1) What happens really?
2) Can I set it to maximum so it doesn't turn off. Will it affect drive health?

 

[Bolin]

it turns off the hard disk, if you want to access something inside the HDD you have to wait for it to start spinning again

 

[boosted1g]

A hard drive has a little motor in it to spin the disks.

This uses power for 1, and for 2 the motor has only so many hours (hundreds of hours) of life in it, so the more it runs the less life it has.

Thus windows automatically turns off the drive when it is inactive for a period of time. This causes a very momentary delay when coming back to your computer but only does good and not hard to your drive.