There are three core use-cases for performing profit center reorganization.
Introduce profit centers to your system.
It could be that you don't have profit centers set up in your system but you plan to start using them. For this, you need to create all the profit center master data and assign them to all the different objects such as materials, cost centers, assets, etc. You would use the profit center reorganization tool to change from an empty profit center to a new profit center. Based on a validity date the tool updates and assigns profit centers to master data and also transfers the existing balance sheet values to the new profit centers.
Correct wrong profit center assignments.
You might have created a material master record and assigned the wrong profit center and even just an hour later you figured out it was the wrong profit center. You need to change it but someone else already created a purchase order for it. There is no chance to change the profit center directly anymore in the material. You use the profit center reorganization tool to define a reorganization: you enter the material and the new profit center assignment and directly process the correction. The tool then updates the profit center and the master record and checks to correct the inventory total. This is typically a scenario that focuses on only a few objects, not thousands of master data. In the case of corrections, you might not have an explicit reorganization date, so, there is no need to perform this at the beginning of a year or at the beginning of a period.
Reorganize the organizational structure of your company.
Complex reorganizations, when you need to replace and reassign profit centers in many and many types of master records will have a major impact on the profit center and balance sheet reporting. For these it's always best to have a clearly defined reorganization date, usually the start of a new financial period, so that the profit center balance sheet reporting has a clear separation. The tool takes care of the profit center replacement in all master data and performs transfer postings along the value chain. For example, for a material, the system updates not only the material master, but also all relevant purchase, sales, and production orders. It also performs the required transfer postings in inventory, including the work in progress and the goods received ensuring the consistency of the balance sheet values.
The use cases all only support transfer postings for balance sheet values. The tool doesn't transfer profit and loss values. The history of the profit and loss is always maintained.