In the power settings, all 3 power profiles turn the hard disk off after 20 minutes of inactivity. Does this disconnect you from instant messaging or cause other problems like software crashes? Also does this stop programs like disk defragmenter, anti-virus, or defender from working correctly? Thanks.
It shouldn't cause any network disconnections or other problems. When there's activity and the hard drive is needed it will spin up. Windows caches files in RAM and also can delay writing files to the drive, so it can still operate until a new file is needed. There are some background services like search indexing and windows update checking that require hard drive use. I think it will wake the drive up on its own to do those things. The downside of having the disk go to sleep is when you're ready to start using the computer there may be a pause while it spins up.