Understanding the relationships between different requirements is important to ensure that there is an understanding that some capabilities may, in and of themselves, provide limited value to the organization but need to be delivered in order to support other high-value requirements. 

Let's look at a real-world example.

An organization wants to implement a fully integrated call center solution. In order to be able to implement this solution, they need to replace all existing phone handsets because the existing handsets are not compatible with the special integration requirements for a fully integrated call center solution.

In this example, the organization has no need for new phone handsets as such; however, this has been identified as a requirement dependency. Therefore, it must be included in order for the call center solution to be fully functional when implemented.