1\ link in the metal chassis to achieve electromagnetic shielding and safety protection purposes;
2, pcb circuit board **** ground can be connected to the ground terminal, but be very careful, set up to a lot of circuit problems. For example, the circuitry of the TV set must be suspended **** ground. Hence the reasoning that for a long time TVs had to be two-pin plugs.
Also, for example, the grounding of the stereo is also very delicate, and can never be simply PCB simply connected to the ground terminal.