Monopoly avoids duplication and hence wastage of resources.
A monopoly enjoys economics of scale as it is the only supplier of product or service in the market. The benefits can be passed on to the consumers.
Due to the fact that monopolies make lot of profits, it can be used for research and development and to maintain their status as a monopoly.
Monopolies may use price discrimination which benefits the economically weaker sections of the society. For example, Indian railways provide discounts to students travelling through its network.
Monopolies can afford to invest in latest technology and machinery in order to be efficient and to avoid competition.