Reductionism isn't necessary for every day use. But it is preferred as it will tell you when things might change. Trends/formulae derived from simpler well tested concepts are more stable.

Take for example the long term trend of world economic growth. It is a good day to day expectation that the world economy is growing, however If we could reduce it to a function of population growth, energy supply growth and new technology we would have a better idea of when we might stop getting the fairly reliable historic growth.