Every app instance is reachable through a private, secure path rather than sitting on an open port facing the internet. You get a working URL for your app without having to think about exposing it safely yourself.
This matters most for applications that don't natively support the kind of persistent, real-time connections modern web apps rely on - the tunnel is built to carry those correctly, so features like live chat updates or a responsive in-browser editor don't quietly degrade to slow polling because the connection in front of them wasn't configured for it.
See the app-specific guides - Rocket.Chat and VS Code Server in particular - for where this shows up concretely.