Blastula cells are stem cells, why is this so important?

A single-celled zygote will undergo multiple rounds of cleavage, or cell division, in order to produced a ball of cells, called a blastula, with a fluid-filled cavity in its center, called a blastocoel. In animals with little yolk in the egg, the zygote undergoes holoblastic cleavage, in which the entire zygote is cleaved repeatedly; in animals with a lot of yolk in the egg, the zygote undergoes meroblastic cleavage, in which only part of the zygote is cleaved. The blastula eventually organizes itself into two layers: the inner cell mass (which will become the embryo) and the outer layer or trophoblast (which will become the placenta); the structure is now called a blastocyst. During gastrulation, the blastula folds in on itself to form three germ layers, the ectoderm, the mesoderm, and the endoderm, that will give rise to the internal structures of the organism.