Gives a unified view of the universe. Makes a person a more critical thinker. The usefulness of deductive reasoning depends on how true the original axioms are.
Geometry is a good example of the use of deductive reasoning.
This is known as empiricism. For example, I observe that a very hard rain falls at the rate of 1 inch per hour. Supposedly, Noah's flood lasted 40 days. Hence I can use the inductive method to test the validity of Noah's flood. Continuing at the same rate of 1 inch per hour, two feet a day can fall each 24 hour period.