In a 3D model, an isolated vertex is a vertex that is not attached to a face. Isolated vertices sometimes result from complex modeling processes or from importing models from CAD applications.
While isolated vertices don’t usually cause rendering problems, they can often break a customer’s workflow. For example, the skinning process for a rigged character often relies on numbered vertices, which means isolated vertices can add unnecessary confusion and potential errors to the process. This problem is particularly frustrating for customers because it’s easy for you to fix before you publish your model for sale, but it might take the customer hours to detect and fix the problem after they buy.