7/24 computer power on, is it bad for the hardware's lifespan?

You are free to power your PC how ever you want. There isn't any study or definitive proof that leaving it on is good or bad for the system.

I currently have two PCs. One is a HP 1aptop 15-dw0xx (W11) and the other is a fairly old HP Pavilion (W10).

With the laptop, I close the lid, and put it in hibernate, when I am not using it. I like this way because, when I open the lid and hit the power button, I'm ready to go in 15-20 seconds. The only time I reboot is when there is a update available. Currently, there is a update (kb5036980) waiting to be downloaded/installed. When convenient, I will download/install the update and reboot.

The HP Pavilion stays on all the time. It's been running 24/7 for about 8 or 9 years. I let any updates be installed, as they come. I use a wireless mouse and keyboard with this PC. When I am done working with it, I just turn off the mouse and keyboard. In a little while, the monitor will blank, all by itself. To start up again, I just power on the mouse and keyboard and hit the escape key. Everything is ready to go.

There will be a lot of users that will say they keep their PC running all the time and never had a problem. Or vise versa. But a sampling of one or two is pretty useless. Before I retired (2011), I was the lead Unix administrator for a very large company, for over 20 years. There were only about 5 or 6 of us to take care of around 600 Unix systems. There was an equal amount of PCs running some version of Windows. The Unix systems were a mixture of Sparc and x86 devices. All systems were left running 24/7. Many of the important servers were protected by a UPS system, with automatic switch over and diesel generator.

Over those 20 years of service, I can only remember 2 or 3 systems going down due to burnout. Mostly, systems were replaced/updated simply because they were old. Some were pretty slow, but supported programs that were still partially active. I remember having to dig up a old Sun 1E VME system (Sun 3 - 68000 based) for a program that included "spare boards" for a foreign country's radar processor. The program itself was 20 years old, and ran when was on assignment in another country. It took me a month of scrounging (the company had around 1,000,000 sq ft.) storage areas and checking old 9-track tapes, to dig up the old software and hardware and get everything working again. But when I got it all together, it all still worked. The company made a bundle supplying spare boards for the foreign system. The program manager got a lot of "atta boys" for pulling it off. But for me, it was just part of my job.

NavyLCDR said:

Start and stop cycles cause more wear and tear on HDDs than hours running.

Really? I would have thought that constantly running would wear the bearings prematurely.

I learned something today.

cereberus said:

What's an HDD😁.

A spinning old style antiquated hard drive, she said, looking at her PC full of SSDs.

Steve C said:

If you believe that then you should disable HDD power saving which spins down the disks

And I did on my NAS until I replaced them with SSDs.

Catnip said:

Really? I would have thought that constantly running would wear the bearings prematurely.

I learned something today.

seriously? the first time I have ever heard that theory. spinning up causes more wear imo

modern HDD specs are meant to be 100,000 hours, which if powered on 24/7 (which they often aren't) gives 11 years of running time. spinning a disk up daily will cause far more wear imo than leaving it spinning for days or weeks on end (sure, switch it off if it's not going to be used for a week or so). I did once damage a 7200 RPM drive (faulty sectors), but that was because I put it in a silent enclosure without airflow and insulated from the metal case which caused it to overly heat up

to answer the original question - keep dust off heatsinks, remove dust from in or out-vents and fans running dust free to remove heat is probably the most important thing I've done (as well as not physically bashing it). putting a blob of heat paste occasionally onto the cpu probably doesn't hurt