[Stierlitz]

"When the telex was sent, once the connection was made, the paper tape was played back to the receiving telex. In this way the message would not be hindered by slow typing with mistakes."

The purpose of using paper tape was to keep both machines in synchronization, something difficult to achieve using a human typist.

"An introduction to Creed Teleprinters and Punched Tape Equipment"

http://www.samhallas.co.uk/repository/telegraph/