Other than your refrigerator, the only thing in your house that you might never bother turning off is probably your computer, especially if it's a desktop. But if you're one of those folks that leaves your PC on 24/7, are you shortening its lifespan prematurely? Or, are you actually doing it a favor?
Let's first look at which components in your PC are most likely to wear out from prolonged use, starting with the capacitors. You know, those things that look like little water towers and store electricity? You'll mostly find them on your motherboard and inside your power supply, as well as on your graphics card and other expansion cards.
Low quality capacitors used to be more common, but after the infamous capacitor plague that saw lots of computers die prematurely in the early to mid 2000s, we're talking less than a year in some cases, component manufacturers have started taking capacitor sourcing much more seriously.
For instance, even lower to mid-range motherboards these days mostly use solid capacitors, which typically have a rated lifespan of over 22 years of continuous use at 65 degrees Celsius, which is quite a bit warmer than motherboards usually get. At lower temperatures, capacitor life is even longer, a lot longer.
Now, cheaper liquid electrolytic capacitors don't have life spans quite that long, and it turns out that these are commonly used in even high-end power supplies. But the good news is that not only do power supplies usually run at moderate temperatures, but those chonkey primary capacitors can still last for upwards of 15 years even though they aren't solid caps. And this stands even for cheaper units, so long as you didn't get a no-name model from the bargain bin.
So unless we're talking extreme heat, your capacitors are probably fine, but what about the rest of your parts? Well, computer fans can have a fairly limited lifespan, specifically, cheap, sleeve-bearing fans, often found in lower-end builds, can die after about four years of continuous use. Nicer ball-bearing fans can last about twice as long, but regardless of what kind of fans you have, the good news is that if they do die, they aren't typically expensive to replace and also shouldn't result in your components immediately overheating unless you've got some serious ventilation issues from dust.
But, there is one component you should keep an eye on, is the venerable hard drive. Although SSDs have become a lot more common, hard drives are still used for cheap mass storage and are often still included in low-end prebuilt machines. Because hard drives have moving parts, it's usually a good idea to replace it after about five years of power-on time. And fortunately, you can keep an eye on your drive's built-in smart data to check if a hardware failure might be in your future and move your data accordingly.
Your computer's other components such as the CPU and the RAM actually more likely to simply become outdated or obsolete before they actually die, even if you leave your PC on 24/7. But beyond simply not doing much harm, leaving your computer on can have advantages. For example, assuming you have the correct settings enabled, leaving it on can allow the PC to perform updates while you're away. So when you come back, you could do whatever it is you typically do without being interrupted.
Having it powered on is also necessary for remote access, for using it as a server or a router, or for background activities like crypto mining. But at the same time, we are not telling you to just leave your machine on all the time without a good reason. Turning a modern PC off and on several times a day is not gonna wear out the components, and running a computer will accumulate more dust and, of course, draw more power than one that's turned off. That's something we should all be thinking about seriously.
Finally, you can have a sticky situation on your hands if something vital like a CPU or a GPU cooler dies while you're away from your PC, not paying attention. But the bottom line here is that nothing bad is likely to happen just from leaving your PC on all the time. But make sure that you do turn off the monitor while you're away, as those can die before your PC does.