Why are unsaturated hydrocarbons more useful than saturated hydrocarbons as starting materials in chemical manufacturing

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon,[1] and thus are group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls. Aromatic hydrocarbons (arenes), alkanes, alkenes, cycloalkanes and alkyne-based compounds are different types of hydrocarbons.

The majority of hydrocarbons found on Earth naturally occur in crude oil, where decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can catenate to form seemingly limitless chains