Asymmetric cell division:
All of us were once a single cell, when we came to an existence in this world. Since then, we developed into individuals composed of trillions of cells, made of neurons, skin cells, gut cells, muscles etc. Asymmetric cell division underlies diversification of cell types, starting from a single cell, fertilized egg. Thus, understanding asymmetric cell division will lead to understanding the development of our life.
Satellite DNAs are the least explored portion of our genome. Composed of mainly repeat sequences of various kinds, their function remains mystery almost entirely (or some think that they have no functions at all). We believe that satellite DNAs play fundamental roles in cell division and development. Exactly how? We don't know that yet---that's why studying satellite DNA is extremely exciting.
Many thinks that germ cells are not "essential", becasuse we can live without them. Really? Without germ cells, we don't even exist. Whereas our somatic cells are eventually worn out (that's how we age and die), germ cells somehow can be passed on for generations after generations. Germ cells are immortal. What makes it possible and how germ cells achieve such a feat (and why somatic cells cannot/do not do the same) is a fundamental question in biology. Understanding germ cells is understanding life. That's why we are so interested in biology of germ cells.