According to the BABOK® V3 Guide, the purpose of assessing enterprise limitations is "to determine how factors external to the solution are restricting value realization."

When we consider the external environment of a solution, we should consider its interactions and interdependencies, as well as other environmental factors that exist outside of the enterprise.

Enterprise limitations can even include factors such as culture, operations, technical components, stakeholder interests, or organizational reporting structures.

In a nutshell, when assessing enterprise limitations, you identify the root causes and describe how enterprise factors limit value realization for the organization. 

Let's consider the following real-world example: 

A complete paperless publishing solution is implemented within a traditional publishing house. The idea is that all core business processes will now only be executed electronically and no more printing of drafts or review copies will be allowed. Therefore, manuscripts that are received into the publishing house will be electronically scanned and recorded, then all editing should be done on-screen. This solution works perfectly on the receiving side of the business; however, the editors are very unsatisfied with the solution as they have always been able to print all the manuscripts to review and edit on paper. They believe that paper-based editing is much more productive and creative and they are threatening to stop work unless they are able to print as they did before.

The core business process here, as well as the organizational culture, is causing a limitation to the effectiveness of the solution, thereby limiting the realization of potential business value.