The flexible connection enables sensors and actuators mounted in the control cabinet to be connected to the SIMATIC S7 more quickly and easily. To achieve this, the front connector is prewired for connection to the digital IO assembly with 20 or 40 individual wires. The clearly labeled individual cores at the other end of the wire bundle can be routed to any element in the control cabinet.
https://www.siemens.com/simatic-tc