Quote Originally Posted by gitcho View Post
Traditional HD's get the best performance when the data is stored in sequential chunks on the platter (ie. the head doesn't have to move all over the platter to read a block of data), but as data is written to the disk, it is not always stored in continuous chunks (may not be free sectors on that part of the platter). Defragging rearranges the data in sequential chunks.

The file structure on SSD's are mapped to relatively random locations due to wear leveling techniques used by the manufacturers to increase the lifespan of the SSD. If you defrag, you'll be doing a whole bunch of reading and writing to move stuff from one random order to another random order, causing wear to the flash in the process.
Not to mention SSDs dont overwrite the data stored in the cells(normaly) so if you format and/or defrag a drive you will see reduced performance since the drive will have to first empty the cell being written to and then write to it. It's actualy quite a large problem with the current technology.

I'm not sure if they've fixed that with the new generation coming out, but it was still a problem 5 months ago when I bought mine from Vertex.