An example would help us understand this much better.
Lets say in an organization there are various events such as trade fairs, training seminars, which occur during the year. Now lets assume for a second that these Trade fairs are organized by the Marketing cost center of the organization. Therefore in this case marketing cost center is responsible for all the trade fairs costs. All these trade fairs costs are posted to the marketing cost centers. Now if the management wants an analysis of the cost incurred for each of the trade fair organized by the marketing cost center how would the marketing manager get this piece of information across to them? The cost center report would not give this piece of info
Now this is where Internal Order steps in .If you go through all cost center reports this information is not readily available since all the costs are posted to the cost center.
SAP, therefore provides the facility of using internal orders which comes in real handy in such situations. In the above scenario the controlling department would then need to create an internal order for each of the trade fair organized. The cost incurred for each of the trade fair will be posted to the internal orders during the month. At the month end, these costs which are collected in the internal order will be settled from these orders to the marketing cost center. Thus the controlling person is now in a position to analyze the cost for each of the trade fair separately. Thus internal order is used to monitor costs for short term events, activities. It helps in providing more information than that is provided on the cost centers. It can be widely used for various purposes .