Let's take William Bradford, the Govenor of Plymouth Colony. He has over 4 million decendents because his kids had kids and so on.
By 1620, when a segment of the church had decided to set off for America on the Mayflower, Bradford (now 30 years old) sold off his house in Leiden, and he and his wife Dorothy joined; however, they left young son John behind, presumably so he would not have to endure the hardships of colony-building.
Dorothy fell from the Mayflower at plymouth Bay and drowned. Later William married and had 4 kids who all had kids and so on. The more decendents a person has the better the chance there is for more people to be a decendent of a famous or royal person.
I am a decendent of Bradford, Charlemange, Pepin the Great, William the Conqueor and more and I bet if we all did our genealogy we'd find more. They are just people to the world at large if they hadn't been where they were to do what they did.
I am also decended from Sarah Osborne a Salem witch who died in jail, the 2 Emerson sisters --- Hannan Emerson Duston, and her sister Elizabeth Emerson both born around 1657 ish and both led very different lives. Look them up and you will facinated.
Genealogy is now based in real science and blood relationships can be proven. DNA has opened these doors as well as the doors to solving new and cold case crimes. There are many other excellent appliciations for it as well.