The neutral wire and ground wire of the live wire, and the three-pin plug has more intermediate and indirect pins, which are connected to the shell of the electrical equipment. Once the electrical equipment leaks, the current flows into the earth through the ground wire, which reduces the potential difference between the human body and the shell and prevents electric shock from hurting people.
Notebooks and other high-power appliances need grounding terminals.
The advantage is that it is convenient to plug in electricity, but the disadvantage is that you give up the protection function of electric shell leakage.