Just watched this wonderful talk by Dave Chinner:

  https://www.youtube.com/watch?v=FegjLbCnoBw

  It  answers  an  important question that I've wondered about for quite
  some time: Why don't provide all file  systems  data  integrity?  They
  care about metadata, but why not the actual data?

  He  considers  this  to be the job of the underlying storage. The file
  system must be able to trust the data it's getting from the  hardware.
  Alternatively, it's the job of the application.

  This  makes  sense  if  you're dealing with expensive, large hardware.
  Consumer hardware, on  the  other  hand,  rarely  cares  a  lot  about
  integrity.

  The  nice  thing  about  ZFS  and btrfs is that you get integrity "for
  free". These file systems always do that, no matter what hardware  you
  use. For me, as a simple consumer, this is important.