Much has been written about overprovisioning and its implementation on SSDs. In short, overprovisioning, or OP, is a portion of storage space on an SSD that is reserved for use only by the SSD controller. The three most common uses for this space are wear leveling, the replacement of bad blocks, and read-modify-writes. Overprovisioning serves to help increase both the longevity and performance of SSDs and it is a very common practice among SSD manufacturers.
However, some users would like to be able to buy their SSDs without the built in overprovisioning and make the decision to OP, or not to OP for themselves. They prefer the flexibility of deciding for themselves when to OP and how much space to use based on their specific needs. Corsair has announced and is now offering SSDs without this overprovisioned space.