Be able to have multiple activities running within the same process. It's not uncommon to have an application that has two activities, i.e. two components of an application. In one use case, having a chart app that is capable of showing a split screen is one such use case, where you can see two views but the application underneath isn't different.
Application modularity – The Android system allows applications that are signed by the same certificate to run in the same process, if the applications so requests, so that the system treats them as a single application. In this way you can deploy your application in modules, and users can update each of the modules independently if needed.