URL Schemes (and intent filters) could be really useful if it was easier for developers to use. Launching another app with a URL scheme is simple if you know the URL but in order to do something useful the app you link to would need some sort of public API you can work with and pass data to.

The most visible, useful, example of URL schemes is Facebook SSO. When a user logs into your app using you Facebook credentials they are redirected to the Facebook app (or website) where it authorises your app and then uses your apps URL scheme to return the user back.