What is the purpose of the diagram of jumper setting?

The jumper settings (if this is the one you are speaking about) are for clearing the BIOS (times, dates, hardware etc...). The diagram is probably showing the settings on which pins to jump when clearing.

Hope this helps.

The diagram show how to set the jumpers for various configuration to suit a variety components that can be installed on the motherboard.
The jumper settings on motherboards are generally for configuring the different CPU clock speeds, the memory bus speed and possibly overclocking etc. Some of the latest motherboards do not need jumpers, the different combinations are configured in the BIOS.