Power, Sex, Suicide by Nick Lane (2006) part 5 "Murder or suicide" mentions that apoptosis has two main functions:
- prevent cancer
- but it is also an important part of body development, e.g. fingers are separated because cells between them kill themselves. Otherwise we would have webbed feet like ducks. There is also a lot of apoptosis during the development of the brain. This has been observed notably in C. elegans see also: Section "C. elegans cell lineage".