Correct, a database feature can't prevent errant developers from posting customer credit card numbers on Twitter either, but compliance auditors won't accept "We don't bother encrypting data because it's pointless!" as an answer. The very real use case here is when private contracts between an end customer and a service provider says "You are in breach of this contract if load my data to any 3rd party service that has the ability to see my data, regardless of whether they use that ability or not. You are allowed to use that other service if you extend your audit program to also audit that other service provider according to my standards and report back to me." I've personally seen this situation prevent the use of SaaS. An encryption control like this where the 3rd party doesn't have keys to decrypt the data is considered satisfactory.
