What is the benefit and what is the harm of economic inequality of citizens?

The economic inequality of citizens has its advantages. Each person gets the income they deserve. If a large amount of work is performed with high quality, then you need to receive a good payment in the form of material well-being for this. This is how social justice is established.
But economic inequality can provoke social stratification. People are beginning to divide into rich and poor. In some countries, inequality is so strong that there is no middle class at all, only the poor and the rich.