This is one of the items that is tested in your Windows 8 App when you use the WACK.

If you are in Southern California, please email this post for more information on getting a token for your app by June 30, 2012!

 

Manages its memory working set to desired targets

Most of the time, using less memory implies you are doing things more efficiently.
Also, when your app uses less memory, the system has more memory available for task switching and it decreases the chances of your app being terminated upon suspend.
The desired working set sizes for Metro style apps are 80 MB for smaller apps, 100 MB for medium size apps, and 150MB for larger apps. These numbers obviously vary per app, but budget your working set to not depart too far from the targets.
Techniques you can use to optimize your app’s working set include:

Upon suspend, release memory or resources that you know will be stale at a later resume.
Decode images only at desired (or reasonable resolution).
Use thumbnail APIs for images when all you need are thumbnails.
Release expensive objects as soon as possible. Don’t forget to call URL.revokeObjectURL

Reference (HTML)

http://msdn.microsoft.com/en-us/library/windows/apps/hh750313.aspx