Defragmenting your computer’s disk is one of the way to prevent your computer from running slowly due to large percent fragmented disk. Therefore, you can schedule the Disk Defragmenter to defragment your disk while you are not using your PC. By default, the Disk Defragmenter in Windows 7 is configured to run once a week on every Wednesday at 1am. If you are always awake during that time, you might want to change it to some other time. To change it,
Step 1: Open the Disk Defragmenter. You can either search for Disk Defragmenter in the search bar in the Start menu OR Start menu > All Programs > Accessories > System Tools > Disk Defragmenter
Step 2: Click Configure Schedule then select your preferred schedule (frequency, day, time, and disk to defragment) and hit OK
My Tech Corner 
Yeah, I agree with your opinion that a simple disk defragmentation can help easily make the computer run faster and insist on regularly defragmenting my computer. I have found a very wonderful article talking something about this as you can see more further information: http://ezinearticles.com/?Disk-Defragmentation—Make-Computers-Run-Faster-Soon&id=3162755.Good luck, everyone!