It's a useful technique if you're not ready to transmit the message yet, but you can safely distribute keys. Think of a spy going out into the field. They car

It's a useful technique if you're not ready to transmit the message yet, but you can safely distribute keys. Think of a spy going out into the field. They carry a booklet with the key. As messages arrive later, they progressively go through the booklet to decode them. The messages are perfectly secure over the wire. It's not useful or practical in many situations that we associate with cryptography over the internet, but it certainly has its applications. Almost every other cryptographic scheme exists in order to increase convenience, at the expense of some security. The one time pad method is "perfectly" secure (assuming the key is securely generated, and kept safe), everything else is less than perfect (although computationally improbable).