You can prevent your computer from freezing, slowing down, and/or crashing in long term!
The Problem with Disk Defragmenter being scheduled to defragment your hard disk weekly by default is that most of the time it skips it almost every week for many months to come!
That's why the computer's performance and the hard disk's health status is almost never maintained, but when its scheduled to defragment daily it will defrag your hard disk at least twice a week during normal computer use, and the best part is that it will be unnoticeable when its doing it.
That way your files will stay in the right place on your hard drive instead of spreading around from one end of the hard drive to other or being broken down into dozens of pieces like a puzzle(one part of a file at one end, one part of the same file at the other end of the hard disk)!
This will basically prevent fragmentation, file loss, blue screen crashes due to hard to read and process data and etc...
And then every time you try to do a simple task such as downloading a file you wouldn't have to wonder around why it takes forever, why your computer all of a sudden begins to make loud noises until loads up or even why it gets stuck at 99.9% when you are downloading a file at very fast speed and etc...!
When you schedule to defrag your computer to lets say 1:00AM, it doesn't mean that you have to keep the computer up till 1:00AM to defrag!
What it really means is that when you turn the computer ON during normal time of the day it will realize that it didn't defrag your computer yet during the day so it will defrag automatically during the day when you are not doing too much on your computer(check email, play videos, chat ant etc...)!