The smartphone only has a 4-inch display on average. It's not like I can open multiple apps and set them side by side--with Word Mobile on the left of the display and on the right. No. Due to the inherent limitations of the screen real estate, multitasking on a smartphone amounts to switching between apps.

The approach taken by Microsoft allows "Mango" to achieve the result while conserving battery life and reducing the impact on processing and memory resources. As long as the app remembers its state and picks up where I left off, I don't really care how it multitasks in the background when I'm not using it.