One aspect of this is that it is easy to abuse. Three20 (the framework currently backing the iOS app) has an implementation of the launcher control but doesn't provide support for the zooming launch animation.
As a result, we've seen apps like rdio using the launcher in a way that goes against the user's expectations of how a launcher should work. Instead of zooming the controller in from the center of the screen, the controller gets pushed onto a navigation stack. In rdio's case, they should have built a simple table view with each 'sub-application' having its own row. Tapping one of those rows would then push the controller onto the navigation stack in the same way that it currently does with the launcher.
--
From a holistic user experience applications "spring forth" from the system launcher, creating a consistent feeling of two functional modes in the operating system. The first being finding and launching applications, the second being using the launched application. Introducing a third layer of launched sub-applications complicates that model, oftentimes unnecessarily.
As a result, we've seen apps like rdio using the launcher in a way that goes against the user's expectations of how a launcher should work. Instead of zooming the controller in from the center of the screen, the controller gets pushed onto a navigation stack. In rdio's case, they should have built a simple table view with each 'sub-application' having its own row. Tapping one of those rows would then push the controller onto the navigation stack in the same way that it currently does with the launcher.
-- From a holistic user experience applications "spring forth" from the system launcher, creating a consistent feeling of two functional modes in the operating system. The first being finding and launching applications, the second being using the launched application. Introducing a third layer of launched sub-applications complicates that model, oftentimes unnecessarily.