If you turn the computer off, you probably save on power. But turning the computer on and off everyday potentially could cause extra wear of parts. This could cause components to fail early.

In addition, Anti-virus programs, along with multiple anti-spyware applications, and Windows require updating. Often, the updates are done on a daily basis. It's important to do this automatically and immediately. Hackers move very quickly to reverse engineer these updates. They use what they learn to attack unprotected machines.

The most convenient time for running automatic updates, anti-virus and anti-spyware scans, and backing up computers is when the computer is idle. You can do all this while you're using the computer. But that would likely bog down the system and take up your time.

If you do leave your computer on all the time, you should probably restart it every other day. This helps clear out the memory.