Do you see those little dots and “resuming” when switching apps in Windows Phone often? It’s not you or your phone
Taking the general performance of some of those apps aside for the moment, one of the hindrances that existed was speed with which these apps would operate within the operating environment itself.
If you have ever owned or used a Windows Phone, one of the common occurrences was some applications would have to re-boot, even if they were recently used. As multi-tasking in Windows Phone 8 improved, the issue persisted, “resuming” might appear between switching apps along with those tell-tale dots gliding across the screen. It may only be for a few seconds, but with today’s modern gear, it is frustrating.
With Windows Phone 8.1, Microsoft introduced a developer feature called “fast app switching” (FAS), also known as “fast resume.” This feature is designed to allow applications to resume faster, without the dots and the “resuming” advisory. It is also requires recompiling the apps to work on Windows Phone 8.1.
As it happens, not all the apps you use in Windows Phone may be compiled for 8.1, and that is why you might still be seeing the dots, even on newer hardware like the Lumia 1520 or Lumia 930.
All this means is that it is up to the developers to recompile their apps to Windows Phone 8.1. It is somewhat understandable that this is not being done en masse because the 8.1 update is not deployed across the board. Apps that are compiled for 8.0 will work in an 8.1 environment, but not the other way around.
Even Microsoft, with its in-house developed apps, is not fully on board, likely for the aforementioned reasons. The good news is that the updates are rolling out at a pretty good clip, and once things are reach some determined tipping point, expect to see applications running a little bit faster as they get updated to operate in the new environment.
sources: All About Windows Phone via Gigaom