Regression is going back in time to an event real or imagined to get todays perception of an historical event. 
 A regression session need be used  to recall an event or some information that is required and relevant for the present.  Regression is really to give someone the permission to make changes in their life by positively utilising some information from the past.

Regression can also be used to memorise a desired positive state that an individual was at previously.  Examples of this is remembering a language they used to speak, an instrument they used play or someone who lost the use a limb to take them back to the time when they were able to use it eg a stroke victim.