It is the morality principle which is formed at the end of the phallic stage at 5 years old. This tells us our sense of right and wrong, it represents the moral standards of the child's same-sex parent. It also punishes the ego for wrongdoings through guilt.
It is satisfying an impulse with a substitute object that is socially acceptable. For example, sport is used to put our emotions into something constructive.
It is a way developed as suggested by Freud in which each stage is marked by a different conflict that must resolved to move to the next stage. An unresolved conflict will lead to a fixation. The stage in which a child is 'stuck' will carry certain behaviours associated with that stage.
This was a huge influence on psychology which was a dominant approach in the early 20th century.
It is used to explain a wide range of things (personality, moral development & gender). It highlights the connection between childhood relationships with parents and later development.
The approach is not falsifiable which means it cannot be empirically tested (according to Popper). Some may argue that it makes it a pseudoscience rather than a real science as it can not be tested.
It enabled therapy to be developed (psychotherapies). Furthermore, there are techniques to access the unconscious (dream analysis and hypnosis).
Additionally, it aided in the development of modern psychotherapies some of which have had success. However, it has been criticised for being inappropriate and even harmful for people with severe disorders.