Mine's only been on for at most a couple hours. I use a laptop not a desktop. Damn though.. 448 days uptime :0
From: Lipcot
isnt it bad for a PC's life to have it ALWAYS on ?
TLDR at the bottom.
Yes because circuits have a lifetime and the more they're used, the faster they burn out or fail (most laptops give a warning when using performance mode or when the display brightness is extremely high as it will reduce battery lifetime and display lifetime).
What a lot of companies do is have two or more servers running in parallel. When it's time, they shutdown one and let the other one take the load and vice-versa. When the servers are under high pressure, they have a load balancer that evenly spreads the load across a set of identical servers/machines. The load balancer CAN let some servers rest for a short period of time while others do the work as well.
If you ever notice, stack overflow and some other sites actually go down 1 hour every day for "maintenance". Not sure what they do during that time though.
But leaving on a computer too long will ruin its life-time. Especially laptops. Servers are usually designed to be on long though and the components are usually hot-swappable/pluggable in case something goes wrong and also have daily/nightly/weekly backups.
P.S. I'm not talking about standby or sleep (which shuts off the power to everything except RAM) or hibernation (which saves everything to disk and shuts down completely).
TLDR: Yes it can shorten the lifetime of your components/computer. Besides, some functions in Windows don't work when the computer is on too long.