The "power management" stuff got really popular when "portables" and "lap tops" became more common. If you want anything approaching decent operating time off of batteries, you really need a system to save all you can.

There are lots of opinions and few facts about what's best for a normal "office" machine.

I tend to agree with what seems to be the prevailing notion that for modern displays, the voltage shock from turning the display on and off does more damage than just leaving it on. Under normal circumstances, the current phosphers will outlast the rest of the monitor, so even "dimming" or "blanking" the display are probably not really necessary. (Screen savers are completely unnecessary as a protection for the monitor on current equipment - but they have other valid uses.)

For hard drives - in the olden days of 5 or ten years ago, most data losses from hard drives seemed to be caused by "hard landings" during shutdown, or "take off skids" during startup. Thus if your main concern was protecting the data, you left them running, even if it did cost a little in total lifetime of the drive. It's likely that manufacturers have solved most of the problems related to the heads "rubbing" stuff off the disks, so the most likely cause of failure is just wearing out the bearings, or failure of the built-in circuits. A good set of bearings, properly installed, won't wear out - unless some crud gets into them. Hard drives are sealed, but are not hermetically sealed, meaning that air, and sometimes other junk, does go in and out. Allowing the drive to overheat can break down the lubricant, which then acts just like someone threw sand into the bearings.

A bearing running at nominally constant speed and load will push some of the crap aside, to make it's own clean ball track; but when the drive starts and stops, the "track" within the bearing changes and the balls may pick up damaging dirt and move it back into the track. So starting and stopping may still damage the drive more than leaving it running.

I have not purchased a new machine in the last 20 years that didn't come with hard drives from the same sources I would choose if I bought them separately, but I don't know what "cheap" drives may be available - since I haven't been interested in getting (an inferior) one.

If your hard drive spins up and then spins down every few minutes, you apparently have a "partly on" power management system. If you turn it OFF completely, the disks should run continuously. If you hear "disk noise" when they power up and down, it's also possible that what you're hearing is actually (at least partially) fan noise. Many newer computers use "managed cooling" that's coordinated with the "managed power," so that the fan speeds up when the drive starts.

Whether to use power-down features, or which ones to use, is pretty much a matter of personal preference. My machine is meant to be used, so when I turn it on, I want it ON, and when I turn it off, it's off. I only (usually) turn off when I'm going to be away, and because of our weather - if it's off it's usually also unplugged.

John