Software DOES NOT tell a HD to park it's heads, not in the last 10 years or so since stepper motor HD's (hardly any made larger than 80Mb)
The heads park automatically because they are voice coil driven which is electro-magnetic. Remove the electricity and the heads automatically return to the parked state.
Unplugging a HD while it's on may damage the electronics, yet I've never damaged one to date, I have unplugged them whilst on hundreds of times (it may fail if it's a WD but thats most likely not because of unplugging it while it's on 🙂)
You cannot plug a drive back in while the system is on however.