The wiring diagram shows how the wiring is physically laid out.
The schematic is a simplified depiction of how the circuit is electrically designed. (How the loads are connected to power, where the switches are, how the loads are laid out in relation to each other – in series or parallel – etc.)
They are obviously related, but the schematic is much easier to use for understanding how the circuit functions, and for doing a load analysis.
The wiring diagram helps you to locate a particular part of the circuit wiring in the machine.