In my opinion the film is a tragedy. I believe many of the comical elements are added in because in times of trouble many people try to be happy by things such as humor. It is a way to tell a tragic story in a less upsetting way.
They provide oxygen
They provide shelter for animals
Angels of death is sooo good you can watch it on crunchyroll,funimation,and Hulu. Erased,Flavors of Youth,The promised Neverland,Cells at work(really good one if your have a hard time in science) I watched those on Netflix:)