Its a good idea to leave behind information that is not necessary for us any more like past phone numbers and names of strangers whom we may not meet again. Episodic Memories

Episodic memories are the autobiographical events of a person's life based on his or her experiences, relationships, learning and ideas. In a loss of episodic memory, the links that exist in the temporal and frontal lobes of the brain are broken. This happens when the patient has suffered a head injury or has been in any form of trauma. Also, episodic memory failure happens when the frontal lobes are damaged and as a result, the patient is able to remember some information though not in the order in which it happened. Further more, this leads to false recollection of events that could not have happened.

Implicit memories

Implicit memories are those that do not require intentional remembering...

The cerebellum part of the brain is involved in motor skills learning and when this part is damaged, it becomes difficult for patients to learn or recollect motor skills thereby leading to an implicit memory failure. Also, the basal ganglia is another part of the brain that is responsible for sequencing actions in the right order and when this is damaged, it has an impact on the implicit memory. This is why amnesia patients have no problem in learning new motor skills because their cerebellum and basal ganglia remain unaffected.
References

Gibb, Barry. (2007). The Rough Guide to the Brain. New York: Penguin

Squire. L; Kandel. E. (2000). Memory: From Mind to Molecules. New York: Scientific American Library

Schacter, Daniel. (2001). The Seven Sins of Memory. New York: Houghton Mifflin Company.