When you consolidate servers and applications, network consolidation is usually either a big issue or not an issue at all. When you collapse data centers and concentrate servers and applications into fewer physical locations, there may be a severe impact on the network. This impact must be evaluated as part of the consolidation project. You certainly need to ensure that there is sufficient network bandwidth to handle network traffic to and from the consolidated location.
Conversely, when you do a rationalization within a single data center, you often find that there are no major network changes that need to take place. The overall traffic does not increase, since new servers and applications are not being introduced. Further, rationalization may actually decrease network traffic, because applications in a single instance of the OS don't need the network to communicate with each other.