If there are 3 or more crease edges ending at a vertex, then that vertex must be a “corner” vertex. There are a few situations where a corner vertex is useful, but in general they are a pox on the surface of the model and best avoided if at all possible. When you encounter a “3-crease corner” situation, you may wish to try using the Rhino RemoveCrease command to reduce the number of incident creases to 2.