DEATH FOR ADULT HOMEOSTASIS. “Programmed cell death is also crucial in the adult, by allowing tissue homeostasis, elimination of damaged or abnormal cells, and defense against infections. It may also play an important but poorly explored physiological role in metabolism, by allowing energy recycling through the ingestion of dying cells by neighboring cells.”
http://www.nature.com/cdd/journal/v9/n4/full/4400950a.html