Adding a layer from another map does not create a copy of that layer, it just makes that layer (data) accessible from this map as well.
Adding a layer from another map does not create a copy of that layer, it just makes that layer (data) accessible from this map as well. Both maps reference the same layer data, and updates to that data (from either map) will automatically appear in both maps. The layer configuration in Layer Settings is map-specific, however, allowing you to configure the layer as you would like for each map independently. The only section in Layer Settings that is not map-specific is the Fields section.