Decision trees help to simplify decision making. It also helps in tracing the steps to develop a solution. Often computer programming is broke down into a decision tree in order to help facilitate the writing of code.
it also helps to develop a standard procedure when running an experiment in the science realm. Does chemical A react with B? If yes proceed here, if no proceed elsewhere.
One such example from wikipedia would be, "In the game of "20 Questions", the querent tries to construct a short binary decision tree that isolates a specific item. The item's identity question is asked when the current decision tree node is considered reliable by the querent."