I had to do a study for my employer back in the 90's.
What I found blew my mind: a single computer costs around $200 a year to run when left on 24/7. Turning it off at quitting time reduces that cost by 2/3, which more than offsets any perceived cost of doing so.
And reliability statistics? Virtually identical. The PC's that were left on 24x7 didn't see any reduce maintenance needs compared to the ones that were off at night; in fact, the ones that were on all the time had more dust inside. That was the only real difference.
For home users, the difference is even higher, especially in the summer, where cooling a PC can add 1/3 of its cost of operation.
If your PC uses 100 watts of power while running, then it's using a kilowatt-hour every 10 hours. That's 2.4KWh a day, or 72KWh a month. If you pay roughly 25c per kilowatt-hour, then that's $18 per computer per month.
In the summer, with the AC running, you must also suck out the heat that computer generates. Over the course of a day, an air conditioner takes around 1.2 kilowatt-hours to remove the computer's heat, increasing our cost by $9 a month (on months where you have the house closed and the AC on all the time.)
That adds up to something like $250 a year in electricity.
On the other hand, if you turn your computer on when you get home, you will probably use it for about 4-5 hours before bed. That reduces your power usage to .5KWh per day on weekdays and maybe 1.25 on each weekend day, or 5KWh per week, or 260KWh per year. At 25c per KWh, that's $65 a year for the computer and around $8 for cooling.
So I turn my computer completely off to save $177 a year. As to reliability numbers? The computer that's on all the time hasn't failed any more or less often than the one that gets turned off. In fact, my work laptop, which gets turned on and off every day and carted home has lasted longer than any of my home PC's. I got it more than 6 years ago, and it's still in use.