it only has to be done if you didn't realize in the beginning that females can only breed up to 50 years old and you breed in bulk in the beginning and didn't pay so much attention with age intervals. because at your estimate, by the time the oldest villager dies by old age, your female villagers (even the youngest one) may be too old to make babies by then. no children, no next generation, the tribe get wiped out eventually. i'm glad i didn't have to do that with mine because i found out early in the game, before i maximize my population, that female villagers have that 50-year-old limitation. so i am able to plan out my villagers age intervals very carefully. it just feels good that the game provides an option, a way to save the tribe when circumstances like the one i mentioned above happens. it may rarely happen though.

i don't think tbug53 has a lot to worry right now. maybe his oldest villager will die in his 70's by old age (mine does). so there's still gonna be plenty of time to make babies with his 14-year-old females, who's going to be in their 20's by then.