Why is the breeding aspect important?

It is one instance that explains everything that happens throughout the movie.

From the dinosaurs escaping to the dinosaurs breeding, much of the events that happen throughout Jurassic Park are meant to prove Dr. Malcolm right when he said "life finds a way."

In this specific example, the Jurassic Park scientists are "spared no expense" and years of research was conducted whereby they did "...things which nobody's ever done before." But we learn that in spite of this massive biologic and engineering feat, where so much deliberate science was conducted to prevent pretty much everything bad that happened in the film, life found a way anyway.