Planning, consolidation, reporting and close software usually requires professional assistance to stand-up. This involves system architecture, data importing and migration, customization, user training, and more. Considering the complexity, it is helpful that the selected vendor has the necessary resources and expertise to handle the implementation without relying on an independent partner network.
Scenario: A mid-sized manufacturing company is looking to acquire and implement a financial consolidation platform. They were burned by third party implementation consultants during their ERP implementation. This time, they do not want to work with anyone other than the software vendor.
Solution: The vendor carries out a needs assessment, plans for the customization according to the customer's needs, executes a smooth data migration, provides robust user training, and ensures a successful go-live. They handle all technical aspects and provide targeted advice along the way. This is all accomplished with their own employees.
It is not always necessary to have the vendor implement the product themselves - in our experience, some of the most competent consultants do not work for the vendor. They're often running their own companies and are sometimes a resource for the vendors on implementation best practices. While this sounds counterintuitive, it is often the case especially with the larger software companies.
Working directly with the vendor does have it's advantages. You'll avoid the blame game when something does not work as expected. You can also leverage renewals or invoice payments to your advantage to get the attention of the appropriate contacts should the implementation hit a rough patch. During negotiations, implementation costs are sometimes negotiable depending on the software spend. A third-party implementation provider has no such flexibility.
Some vendors will sell you implementation services, then outsource those to a third party anyway. If you are uncomfortable with that, make sure to bring it up during scoping.