A plan provides something to measure against, so that you can discover whether or not you are achieving or heading toward your goals. As the proverb says, If you don't know where you're going, it doesn't matter which way you go. Planning converts values to action. When you are faced with a decision, you can consult your plan and determine which decision will help advance your plan best. Decisions made under the guidance of planning can work together in a coherent way to advance company or individual goals.
Planning is useful in emergency situations, too.
When a crisis arises, a little thought about the overall plan will help determine which decision to make that will not only help resolve the crisis but will also help advance the overall plan. Without a plan, crises are dealt with haphazardly and decisions are made which may ultimately be in conflict with each other. Planning allows limited resources to be committed in an orderly way. Their best use can be made when a plan governs their use. A simple example would be planning to buy a house or a car.