Seems like a good idea to me. I just had to learn about it all though.
It's also is used for spares as flash blocks wear out, so while you loose some space you gain some reliability. If you aren't going to have many writes then it's got less value. The write process for flash memory is destructive, it slowly degrades as you write more to it, I've heard of reads also wearing on the cells, but cannot tell you where or why. Over provisioning is mostly to gain longevity, though Quad seems to know more about other uses for those spare cells.
