The NeverAsPin specifier is used exclusively by a handful of animation nodes. Properties of an animation node can be exposed either as pins on the node or as fields in the Details panel. This specifier ensures that a given property can be viewed as a field in the Details panel, and it may also appear as a pin on the node. The UI will contain an eye icon that can be used to toggle visibility of the property pin.
It must be combined with BlueprintReadWrite and EditAnywhere.