Why is Le Chatelier's principle important?
Le Chatelier's Principle is important, because it allows us to shift an equilibrium to the side that we would like to favor. For example the Haber Process produces ammonia reversibly.
The reaction is run at high pressures, because there are 2 moles of ammonia on the product side, but 4 moles of gas on the reactant side (3 mol of hydrogen and 1 mol of nitrogen). Since 2 mol of gas occupies a smaller volume than 4, increasing the pressure will increase the amount of ammonia at equilibrium.
Interestingly, high temperatures favors the reactant side, but the reaction will reach equilibrium faster at higher temperatures, which is why the reaction is carried out at a moderately high temperature.
For more, see: What is Le Chatelier's principle?