Not that I'd use this service for it, but I've had use cases for this sort of thing. It's not so much about plausible deniability as OP wants to sell it as, but more about security. You send the locked link (or a PW protected file or whatever) via, say, email, and the password through a text message. Then, in order for the data to be stolen, the attacker would need access to both of those, rather than only one. It's niche, but I've needed to do it for my job before, so I can at least see the point.