There has been a lot of confusion around Windows, SSDs (hard drives) and whether or not they are getting automatically defragmented by automatic maintenance tasks in Windows. Windows does sometimes defragment SSDs, yes, it’s important to intelligently and appropriately defrag. Storage Optimizer will defrag an SSD once a month if volume snapshots are enabled. This is by design and necessary due to slow volsnap copy on write performance on fragmented SSD volumes. If an SSD gets too fragmented you can hit maximum file fragmentation (when the metadata cant represent any more file fragments)”]
Source: http://www.hanselman.com/blog/the-real-and-complete-story-does-windows-defragment-your-ssd