According to the developer's site
Some devices scale the launch icon by as much as 25%. For example, if the image of the icon with the highest launch density is even more extra-high density, the scaling process will make it less clear. Therefore, you must provide a higher density launch icon in the drawable-xxxhdpi directory that the system uses, rather than increasing the smaller version of the icon.
Note: the drawable-xxxhdpi qualifier is only needed to provide a startup icon that may appear larger than usual on an xxhdpi device. You do not need to provide xxxhdpi resources for all of your application images .
Check out this link for more details http://developer.android.com/design/style/iconography.html
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