What is the difference between grounding and neutral? and what is the advantage and disadvantage if we use grounding as a neutral?

Neutral carries current equal to that carried by the Hot wire. It is the return path for the Hot

 Ground is there for safety, and it should -never- carry current except when something has failed. Even though both Neutral and Ground are attached to the same point inside the breaker box. This is because metal devices attached to a grounded outlet have their chassis attached to the Ground terminal, and if any current flowed through Ground in normal operation, the ground wire could have some voltage on it

GFCI also called GFI outlets and breakers look for any imbalance in the Hot and Neutral current. So if you miswired an outlet so Ground and Neutral were reversed