Network segmentation allows the parts of your network to remain protected from one another.  This is similar to having many rooms in your house that are each protected by a security guard; in order to enter each room, you must first be granted access by the guard.  There is only one way in and one way out, but it’s all part of the same building.

For your organization, this can look like having a separate network for your staff, for your guests/congregation/customers/etc.  There are technical benefits to this setup as well as security benefits.