Updating Software

The most common time for rebooting a computer is after updating its software components. For example, Windows will prompt you to reboot after you install updates from Windows Update. It's not critical for you to reboot, but the update installations won't complete until you reboot.

Hardware Glitches

Sometimes hardware needs to be reset if it's performing strangely. The easiest way to do this is to reboot your computer. Glitches include a storage device that cannot be accessed or an Internet connection that won't stay connected.

Sluggish Performance

On occasion a program will cause a "memory leak," where it steadily eats up system resources until there's none left for normal operation. In this case, sometimes closing the program won't work, and the only way to get those resources back is to reboot.

Other Reasons for Sluggishness

At times a reboot won't help. In this case, you may not have enough RAM (Random Access Memory) to do all of the things you need to do, and you need to install more. Poor performance can also be caused by a virus.

Rule of Thumb

In general, periodic rebooting is unnecessary if things appear to be running smoothly. You should only need to reboot on case-by-case basis, such as in the examples described above.

Source:

Computer Maintenance Overview