Project category in procurement category

Dear All
In the procurement category hierarchy form– an option to assign project category for each category node, but I could not understand the functionality of this feature. How this impact on project module? What if we assign project category this procurement category, where do they have subsequent impact. Can you please assist about this feature.
Regards
Srinivas

Hello,

Maybe this could help you.

Category hierarchies are used to classify products or transactions for reporting and analysis. Your organization might use a procurement category hierarchy to track purchases and a sales category hierarchy to track sales. If you purchase the products that are used for a project from a specific procurement category, you can assign a default project category to that procurement category. For example, you assign a project category named Indirect expense to a procurement category named Office supplies.Your project manager creates a purchase order for a project and selects the Office supplies procurement category on a PO line. By default, the cost on the line is automatically assigned to the Indirect expense project category for the selected project.

https://technet.microsoft.com/en-us/library/hh781064.aspx