From a security point of view:
(1) eliminating leakage. If the insulation of the power supply part is not good, the electric equipment will feel "hemp hand", and it will hurt people. If grounded, the current can leak from the earth wire to the earth, thus protecting the personal safety.
(2) avoid lightning stroke. Lightning arrester on electrical equipment is a device to prevent lightning stroke, so the ground wire must be buried so as to lead the current into the ground.
(3) elimination of induction. Electrical equipment will be subject to electrostatic induction, and the induction current can be safely introduced into the ground if the housing is grounded.