The difference between a schematic diagram and a wiring diagram is amount of detail included. In the schematic diagram, the interconnection of the components is shown, although actual values of the components are not indicated necessarily.
You can see the diagram of a 2-transistor audio amplifier, for instance, with capacitors and resistors and coils and transistors, but without any data concerning the values or ratings of components. This is the schematic diagram, but not the wiring diagram. It gives the scheme for circuit, but you cannot wire the circuit and make it work, as there is not enough information.
Assume that you want to build up the circuit satisfying your own requirements. What are the sizes of resistors which you should buy? How about the capacitors? Dare you required to wind the coils yourself, or can you bring them ready made? Are there test points or other terminals which should be installed for benefit of technicians who might have to repair amplifier? What is quantity of watts should the potentiometers be able to handle? All these things are shown in the wiring diagram. You may have seen this kind of diagram in the end of instruction manual for an FM stereo tuner or a hi-fi amp or a television set. Wiring diagrams are useful and essential when you should service or repair an electronic device.