Apps like Komoot, Strava, Today’s Plan, Training Peaks and TrainerRoad make useful additions to your ride experience. They'll allow you to download routes and workouts, and then upload your ride so you can analyse it afterwards. Having a cycling computer that connects to them will streamline the process of uploading or downloading the required data.
To connect to these apps, your cycling computer will use one of two methods. Either it will connect to your smartphone via Bluetooth, or a companion app will allow the integration with the third party. Or it will connect to WiFi and speak directly to the third-party server (after an initial setup).
However, not all computers will connect with all apps, so check with the manufacturer before you buy. Just because your computer has WiFi or Bluetooth, it doesn't mean the brand has built the software that enables it to connect.