The question frequently arises in organizations:  Who should buy, each area in a decentralized manner or a centralized purchasing area ? Even this discussion serves so that all user areas (internal clients) remember each of the processes in which Due to poor purchasing management a project was delayed or impacted and the purchasing area argues with concepts such as demand aggregation, strategic sourcing, value destruction that end up being so diffuse that it is not possible to fully convince the crowd of areas that detract from the project. shopping area. 

Three types of models are normally evident:

• Centralized purchasing : the purchasing area has a significant sponsor in the organization, normally, who is convinced that the added value comes from a centralization of a single team, managing absolutely all the needs for purchasing materials or contracting services, Getting to this point can be quite tortuous and even worse, maintaining it. It is an ideal point for the supply manager, since he has power in negotiation, knowledge of the organization and in turn is directly responsible for the company’s results. 

• Decentralized purchasing:   in this case each project or area directly executes the purchases of materials or contracting of services and there is a “false” purchasing management where they are only processors or legalizers of processes. In most cases they say they have an equally constituted and recognized purchasing area, but without any decision-making power , they normally process a couple of purchases of office supplies, they have a constant fight for recognition, but it is a very exhausting path. In this model there is a lot of value destruction that is not easy to demonstrate and that generates high impact, due to internal cannibalization of suppliers, prices, market, among others. 

• Mixed model:  in this model the supply area has a defined responsibility for making purchases of some categories and the others have been designated as a responsibility directly to the projects or areas. Although it is not an ideal model for the purchasing area, it can be interesting depending on the quadrant of the Kraljic matriz that deals with supply management:  

1. In both quadrants at the top  (leveraged and strategic) where high impact is generated for the organization, it is the best of all worlds  since management generates high visibility and direct responsibility for the results, managing only one of these quadrants is quite risky. because an important part of the value that can be generated is revealed. 
2. In the lower quadrants  (transactional and bottlenecks), purchasing area management does not have as much value on its own , since it does not generate as much impact and has much less visibility. Addressing these quadrants only makes sense once all categories in all quadrants are being addressed. 

There is a different model, and recommended for large organizations, which may be semantic of the terms used, but normally generate a placebo effect to the different projects and areas that are detractors from purchasing management since they feel control over the supply processes that impact their result; On the other hand, the purchasing area with this model acquires all visibility and responsibility for the result : Decentralized purchases, centralized negotiations! 

This model allows the purchasing area to meet needs, through  planning ,  demand aggregation and design and execution of negotiation strategies  that allow  obtaining common and obvious benefits;  This point includes strategies such as achieving  unified prices  including areas or high-impact logistical provisions that are assumed by suppliers when they have a larger business, achieving  discounts for volume of contracts  in defined periods of time, agreeing on  payment conditions ,  increases /decrements , triggers that  financially impact  the company’s results, generate alliances, among others. For this to be effective and have a real impact, they must be recorded in different figures such as  framework contracts, price agreements, MOUs (memorandums of understanding), electronic catalogs  in such a way that they allow each project or area that has a need, based on clear, transparent, defined conditions and the best negotiations, simply  execute the purchases  under that established agreement.