[BLKNSLVR]

Taking your question conceptually, rather than physically, memories / experience would be 'gunk' if they're outdated (don't relate to how the world works anymore, or don't relate to how your body works anymore).

Your memories and experiences (potentially one and the same) colour your experience of the world and make you react in different ways, not always beneficial - but the phenomenon wouldn't exist if it wasn't historically, evolutionarily beneficial.