Data is written, moved, edited and deleted regularly over the course of a hard drive's lifetime. While that is usually not a problem if the hard drive is pristine, fragmentation can become a issue over time.
Fragmentation refers to parts of files being saved in different positions on a hard drive which can increase loading times.
Defragmentation on the other hand refers to optimization techniques that optimize the file distribution on a hard drive or partition.
While it does not appear to be that much of a problem anymore these days, it is still a good idea to make sure that the fragmentation of your hard drives has not reached levels where it is affecting the performance of the system.
You can use the Windows defragmentation tool for that, or, which many users prefer, a third party tool such as the free Defraggler by the creators of CCleaner. The program offers several benefits over Windows' standard defragmentation tool including the ability to defragment select files or folders only instead of the whole drive.
The program has been updated today bringing the version to 2.16. The application is available as a portable version or setup version, which both work identical after installation of the setup version.
The latest version of the file defragmentation tool brings several enhancements to the application. Piriform has added support for Microsoft's recently released Windows 8.1 operating system upgrade, as well as SSD optimizations under Windows 8.
Two additional feature additions improve the handling of Solid State Drives. The accuracy of detecting Solid State Drives has been improved, and support for Samsung's and JMicron's SSD Trim optimization has been added.
Other new features include the addition of new SMART date to the program's health tab, improved search for locating small files on hard drives, and several minor fixes.
Side note: There is still some confusion in regards to SSDs and defragmentation. The general consensus seems to be that you should not defragment Solid State Drives for two reasons: first because of the write operations that the operation causes, since it may impact a drive's lifespan especially if it is an early generation drive. Second, because Solid State Drives can access data a lot faster than regular hard drives so that the performance gains are minimal at best. Running a Trim command or using the secure erase feature of the hard drive will improve performance by a much larger margin.
In Defraggler, look at the Media Type column to distinguish regular hard drives from Solid State Drives. It is still recommended to defrag platter-based hard drives whenever their fragmentation reaches a level that is affecting performance.
Defraggler does not provide you with any recommendations, but if you spot two-digit fragmentation percentages, you should probably run a defrag on the drive in question.