The Tagged Value definition and predefined types are very useful - boolean, spin (numeric values), enum and much more. We can show the Tagged values in diagrams as compartment. But using Legends is most useful for Tags.
Yes, we can apply Legends with properties or tagged values for connectors. But for connectors, there is a bug in current EA and will be fixed on 15.2. It is better to use 15.2 if you want to use Legends for connectors.