Supply chain planning is essentially about making decisions in the supply chain.
How accurate is our forecast for sales; based on this how much we should plan to sell and produce?
How much materials/components do I need to order from suppliers?
Is my capacity having a constraint? What trade offs we need to make?
Where should I put inventory in the supply chain? Nearer to Customer or nearer to supplier?
What will happen to my customer service if I accept this large order?
What level of profitability will I generate?
Do I need to invest in more manufacturing capacity in three years? If so, where?
Do I need to increase my distribution footprint?
Will I require more suppliers?
And many more strategic and tactical decisions are required in order to manage supply chain operations smoothly.