What is "Regression" and what it is used for?

Regression can't (as far as i know) be used on purpose. it is a psychology term used to describe somebody who backtracks in progress, i.e., an elderly patient who plays with dolls or a toddler who recently started wetting the bed again. it is usually a sign of change, such as a new addition to the family for younger kids, loss of children for elderly, or even or blunt force trauma.