This is always a nagging question in the background of hardware troubleshooting and anxiety.
On the one hand, I lost a PSU for running a system in S3 Sleep-state for weeks at a time.
On the other, I have systems I prefer to keep running 24/7. For everything else, I try to arrange sleep after an hour or two of inactivity, followed by hibernation an hour after that. One system with an 850W Seasonic X-Series Gold PSU was on 24/7 with maybe a week's-worth of maintenance downtime over an entire year.
Using sleep and hibernation wisely shouldn't shorten a computer's life, and might even extend it -- can't be sure. But it will contribute to a lower power bill.
The 24/7 system mentioned above is being recycled for my old Moms. Good . . old Moms. It must sleep and hibernate reliably. It must be configured to wake up from the keyboard. After setting it up for 24/7 feeding my HDTV as a minor function, Sleep at first was tricky and then it was flakey. About 40% of the time, going through its daily cycle of waking, backing up, sleeping and hibernating again, it would fail to restore the RAM contents and throw a message about the hibernation failure and continuing boot without it. If left in that state instead, it would not be available to wake up nightly for backup to the server.
So after some six years of operation, the old 850 Gold X-series has to go. It could have continued usefulness if sleep is eliminated from the equation so that only hibernation and wake-up occurs. But then, what might be the next surprise from an old PSU? Don't need surprises. . . .
I think PSUs will run their life consistently with an expectation of dying across a statistical distribution and a left tail spanning the end of the warranty period. It also makes a difference if you use clean power from a UPS.