The datasheet translates the physical connector into a logical schematic. Without this document, the hundreds of pins on a modern ECU are indistinguishable from one another. The datasheet ensures that an engineer or technician does not apply voltage to the wrong pin, which could destroy the ECU's internal circuitry.
For detailed technical specifications and wiring diagrams, you can explore specialized repositories: bosch ecu pinout - The Datasheet Archive Bosch Ecu Pinout Datasheet