What is disk fragmentation and why does it happen? As files are stored, moved, deleted, updated and so on, over time they can be potentially stored on different areas of the disk rather than in a single block. This is called disk fragmentation. There could be thousands of parts of files scattered all over the disks on your home server. What this means is that it takes longer to read and write those files than it would do if they were all in the same place. That annoying delay waiting for that Word document to open? Could be disk fragmentation.
This is where disk defragmentation software comes into play. The software examines the disk and all of your files, figures out where the parts of the files pysically on your drives are and attempts to move them together to make things run faster and smoother. This is a good thing