If you don't like leaving your PC running 24/7, but you sometimes forget to turn it off, here's a great utility that can help. As you can see from the screen shot below, it offers a great range of timed shutdown features for Windows. You can opt to turn off the PC, or log off Windows, or have the machine sleep or hibernate. You can choose to have this happen at a specific time every day, or just on a particular date, or at a specified number of hours and minutes from now.
The program is called Winmend Auto-Shutdown. It's free, you get it from http://www.winmend.com/auto-shutdown/, it's a 2 MB download, and should run on Windows Vista and above. It's also free of malware, according to VirusTotal.