Why it matters practically

Evolution as a working tool.

Medicine and agriculture

Resistance in bacteria, weeds and cancer cells is evolution in action, and treatment strategy is designed around it. Flu vaccines are updated annually for the same reason.

Finishing a prescribed course and avoiding unnecessary antibiotics slows resistance.
Monoculture crops are fragile because they lack variation.

Beyond biology

Selection algorithms, evolutionary computing and directed evolution of enzymes all borrow the mechanism deliberately. It is a general algorithm that biology happened to discover first.