What happens if the very important directory you copied 11 times (just to be sure) ends up producing the same block and doesn't indeed get duplicated as you expected? And now, that block gets corrupted...
If you're going to make 11 copies, they have to go to different physical locations, different devices at least, geographically different places to be sure, or it's pointless.
In this instance, block de-duping on a single device makes sense .. expecting mutiple copies on the same device (with or without duplicat block reuse) to offer any additional safety does not.