I'll try to explain this as simple as possible; The pump creates hyd flow to a control valve. Let's say the loader control valve. This would be your in port (from the pump). The fluid then travels through the valve if controls are neutral and out of the Power beyond port to it's next destination which is usually the 3ph control valve. As long as the 3ph valve is in neutral the fluid flows back to tank or in most cases the trans case. If you want to add on additional hyd's you just tap into this loop.
If you are reffering to the power beyond kit available for some Kubotas, that taps into the system prior to the 3ph valve and allows you access to the fluid at a more conveniant location. You can tap off of power beyond anywhere in the system because you will have a pressure relief valve usually prior to and or in the loader valve and this will protect the circuit. However, whatever you install into this circuit must be continued back to "tank" in order for everything "down stream" to receive hyd power. Also if not continued, the fluid will "dead head" causing the relief valve to stay open which will over heat the fluid, over work the pump and cause the loader to not work very well, if at all. Depending on the model tractor depends on what sets main relief pressure. The relief valve always has a seperate hose or path back to tank. On most Kubotas this is represented in the color code on the hoses. Orange=from pump, Green=power beyond and Gray=return to tank. Some models take pump flow directly from the pump in which case the loder valve needs to have it's own relief valve while other models have a "hyd block" or diverter valve that contains it's own relief. Hope this makes some sense to you......