When you don't license your app, you are running in Developer Mode. In Developer Mode you'll see a watermark on the MapView and SceneView. All functionality will be available to you.
On the developers website, you can obtain a free "Lite" license. Once you call ArcGISRuntimeEnvironment.SetLicense(licenseString) your app snaps out of developer mode, watermark goes away, and all the functionality that isn't supported in lite mode will throw a license exceptions.
I'd recommend developing your app licensed at the right license level from the beginning, so you don't get caught by license restrictions later on.