not in ohio
The reason why 'fragmentation' is a bad thing on most rotating storage is that, when reading a file, the heads have to move from one fragment to another, and that's a relatively slow mechanical operation (takes milliseconds rather than microseconds).
So, there's no gain from defragging a device which does not have moving read/write heads.
What defragmentation will give you on flash-based storage is 'more writes done' as fragments are moved around the storage: which is, after all, what defragging actually is. Since the lifetime of flash is measured in the number of writes to any given cell, it's not a good idea to waste writes doing something that doesn't help.
So, not only is defragmenting not useful, it costs you very slightly in probable lifetime.
(But don't get totally paranoid about minimizing writes; sometimes the above write-limit gets misinterpreted in some sort of extreme way).