Accurately managing and tracking inventory can be a simple task, but it becomes more complex the more granularity you want from the information.
For every action there eventually needs to be an equal and opposite reaction to keep numbers balanced. If you track orders of stock but do not accurately account for receiving material then you will have open orders showing, and no inventory available on your shelf. If you are producing assembled items but do not manage your Backflush levels then you will have imbalances in your available stock.