Windows – What happens if I stop defragmentation

Measuring the performance gain from defragmentation is rather difficult, however there are some utilities that are meant to "aid" you with it.

There's the utility called File Access Timer, from Raxco, available here. This tool will read a certain file/folder a set amount of times and display how long it took, along with the fragments.

Excerpt from the readme

The File Access Timer allows you to select a file or folder and read the contents several times in order to measure the performance gain achieved through defragmentation. The general process is to select a fragmented file, read the file using Raxco's File Access Timer, defragment the file, and re-measure the time needed to read the file. By doing this you can see the benefits of defragmentation for yourself.