Ultimately, almost every Internet of Things project will, at some level, need to provide a way for the things to deal with humans. User interface considerations can range from a mobile app that allows a user to turn lights on and off and adjust the volume on a music player, to output features such as status monitors, analytics, and data visualization dashboards.
Most providers with a publish/subscribe service for Things will also provide a friendly website and REST or MQTT API’s for you to see and use the data stored. Your end-user applications can be built on top of those APIs to receive device status, manage deployments, maybe even publish messages directly into the event stream. If there’s a mobile app, look for providers that offer native notification support for iOS and Android. Native notifications can give your IoT applications a way to tell the user that something is happening, even while your app is in the background or not running.
There are also many services which are focused completely on analytics and data visualization. You can find everything from turn-key analytics dashboards, to advanced charting software development kits (SDK) that let you build custom interfaces for your favorite platforms and languages. These can be great for industrial and architectural IoT applications where there’s data-overload.
Most importantly, you, as an engineer, may be really great at RF layout - but not so great at UI design. If you can leverage the service’s dashboard, that’s one less thing you have to code up before launching a product.