Sure, let's say you have an organization, in which you have users and devices, so users and devices have a nullable FK to organization. Also, a device can be li

Sure, let's say you have an organization, in which you have users and devices, so users and devices have a nullable FK to organization. Also, a device can be linked to a user, so a device has a nullable FK to a user. Now, when a device is linked to a user, both should be on the same organization, right? I don't see how to easily do that as a constraint (but I have to admit my SQL skills is quite low, and I avoid bypassing the ORM). Well, in production, devices might land somewhere else, and now you have a device that is supposed to be on organization A which is linked to a user on organization B, if you didn't force the organization when a device is linked to a user. Depending on your use case, it could be expected, an operational error, or something that should be resolved automatically. Edit: another example. We have a legacy system. Part of the data is supposed to be mirrored on both new and legacy system, via API calls (I don't know of a better way, I'm not a great dev, DB are different, not shared and on a different provider). Well, check if they are actually the same from time to time (at least the obvious stuff).