The end users are actually the people that will be using Dynamics NAV 2013 on a daily basis. The project will truly succeed if they really use the system. And they will only use it if they think it is reliable and find that it makes their job easier.
For all of this to happen, it is important that they get involved in all the steps of the project from the very beginning. They may not have a responsible position in the company, they may not have the power to take certain decisions, but they definitely have a lot to say.
When we talked about the definition of the internal processes, we said that you had to ask yourself and your people, what were your processes, the activities inside each process, the information used by the process, and so on. We also said that the real processes should be considered and not just the theoretical processes. The ones who actually know the real processes and activities are the end users. If you don't ask them, if you do not involve them, you will not be working with the complete information and thus, you will not be able to define your real requirements.
Even if the final solution really meets all the requirements defined in the project, if those are not well-defined requirements, the project will fail as the end users will not find it useful. Instead, they will keep doing their extra processes, keeping their own information in spreadsheet files, and so on.
The definition of the processes and the requirements is the most important part in which the end users should get involved. If they get involved in defining how they work and how the system should behave, they will really find the system useful and actually use it. But that's not the only part of the implementation process in which they should get involved. It is also important that they participate in the testing process, especially in those functionalities that have either been modified or that have been completely developed. If they participate in this process, they might find errors or any other kind of improvement that could be done to make everything easier. If they bring it to your attention, the Dynamics NAV implementers will be able to fix or to improve the process. If they do not get involved in this process, they may find errors or improvements once the functionalities are live, but they might never tell you. Instead, they will find workarounds to their daily job that will make everything less efficient and more chaotic.