Answer Description

Defragmentation will rearrange the information stored on the disk to increase disk reading speeds. Defrag is not necessary when using Solid State Drives (SSD) but is helpful for performance reasons when using Hard Disk Drives (HDDs).

Wikipedia

Microsoft Drive Optimizer (formerly Disk Defragmenter) is a utility in Microsoft Windows designed to increase data access speed by rearranging files stored on a disk to occupy contiguous storage locations, a technique called defragmentation Defragmenting a disk minimizes head travel, which reduces the time it takes to read files from and write files to the disk As a result of the decreased read and write times, Microsoft Drive Optimizer decreases system startup times for systems starting from magnetic storage devices such as a hard drive However, defragmentation is not helpful on storage devices such as solid state drives, USB drives or SD cards that use flash memory to increase speeds, as these drives do not use a head