The Transfer case is part of a four wheel drivetrain system the purpose of the transfer case is to engage & disengage the four wheel drive when activated and deactivated. The transfer case can be aluminum or steel housing that’s found under the vehicle and the majority of transfer cases are chain based or gear based.
Since there’s moving parts inside of your transfer case routine maintenance is required to expand its lifespan. Draining the fluid from said transfer case and refilling it should constitute for the required maintenance. You should consult the owner’s manual for your vehicle to determine the proper maintenance intervals and the fluid specifications and capacities for your vehicle.