When you look at NIST 800-171 compliance, it has some similarities to the Payment Card Industry Data Security Standard (PCI DSS).
From the perspective of PCI DSS, if scoping is done poorly, a company's entire network may be in-scope as the CDE, which means PCI DSS requirements would apply uniformly throughout the entire company. In these scenarios, PCI DSS compliance can be prohibitively expensive or even technically impossible. However, when the network is intelligently-designed with security in mind, the CDE can be a small fraction of the company's network, which makes compliance much more achievable and affordable.
We feel that NIST 800-171 should be viewed in the very same manner. This guide is meant to help companies identify assets within scope for NIST 800-171 and potentially find ways to minimize scope through isolation or controlled access.