There are several scenarios that might require your site’s content to be encrypted in your database. Student data, medical records, any kind of financial data - any site owner who is storing this kind of information is going to be very interested in encryption.
I ran into an issue a couple of years ago where a site owner wanted all the node data encrypted (it was an educational site, with student data privacy concerns). While this is certainly possible, it created performance and usability problems that finally made the client decide to ditch the whole idea.
Now a Google Summer of Code project has turned out a Drupal module - Pubkey Encrypt - that simplifies the whole process, to the point where it's purportedly not a usability or performance disaster any more.
And so Drupal 8 gains one more leg up...