With traditional hard drives, a majority of the time taken to read and write information is for the head articulator in the hard drive to move the read/write heads to the correct position, then wait for the platters to rotate to the correct position, so that data can be read or written. To improve performance, you want to minimize these seek operations and keep all data that relates to a particular file in a single place on the disk. This is what defragmenting the hard drive does: It takes all the fragments of files on a disk and moves them into a contiguous stream, thus speeding up disk operations.
An SSD has no moving parts, spinning platters, or read/write heads. Performance is the same whether data for a file is stored in continuous bits of memory or scattered throughout the memory.
Therefore, I recommend that you not defragment SSDs, as nothing would be gained and the defragment operations cause additional write cycles on the memory chips. These write cycles reduce an SSD’s lifetime, though not by much