Within an enterprise, there are services (systems really) that are widely popular, offer just what you need, and are easy to use. There are also systems, which for years the organization tries to decommission but they have so many applications depending on them, so many strings attached, it seems impossible. Often, it's the same system, at different points in time.
Recently while exploring a legacy application in order to design its Cloud-native replacement, we identified a connection to such a system. We will refer to this system as the SAK (aka Swiss Army Knife). We wanted to do our part and remove one more string. The SAK’s service we consume acts in essence as a proxy for a database. After investigation, we found out that our application is the only one using the specific data (and thus the service). For the data, imagine a contact list (it's not really a contact list), which facilitates the main business offering of the application. I know I am vague, but I have to be. The data in question make the main functionality easier but their lack does not make it impossible. You could still make calls without your contact list, but it would be a pain. Some clients use the application daily and some might not use it for months.