We all know that the loose coupling provided by Android through intents is one of its most powerful features. It makes it possible for us to mix and match the use of activities between various applications as though they all belong to one.
However, when I want to invoke another application that has published an intent filter, I cannot always assume that the other application is available on the phone. So, I need to check its availability and then only enable the feature to call it.
This is very well explained in the link: Android Developers Blog: Can I use this Intent?