There are advantages and disadvantages to splitting a PCB power plane to meet MIL-STD-461G EMC limits. Some of the benefits split into power planes are as follows:
Split planes separate power and ground, reducing the amount of Electromagnetic Interference (EMI) between these signals.
Split planes allow for separate power distribution to different parts of the board, reducing the effects of power drop and providing a cleaner power supply.
Split planes provide a clear physical separation between signals, reducing the amount of crosstalk and improving signal isolation.
On the other hand, splitting power planes also have disadvantages as follows:
Split plane designs can be more complex to implement and require more layers in the PCB, making them more expensive to produce.
Noise will be introduced into the power and ground planes, affecting signal integrity if the design of the split into the PCB planes implementation is wrong.
Connecting the signal traces on different planes may require routing traces across split planes, which is challenging and would require adding vias and stitching to connect the various planes.