This feature is quite useful in my eyes
For example, Airline A can build a terminal at PEK (for example) but Airline B wants to fly to PEK as well. It happens that both the airlines are in the same alliance. Airline B can choose to use the public gates or the gates that Airline A has in his/her terminal.
If Airline B uses the gates that Airline A has, Airline A needs to approve the request, then the normal gate rules apply. And compared to the public gates Airline B can pay half the leasing price