Apple Warns Retina Display MacBook Pro Owners Not to Use Palm Rest Covers
Apple is warning Retina Display MacBook Pro owners not to use palm rest covers as it can damage the display of the notebook when you close it.
MacBook Pro (Retina, Mid 2012): Do not use palm rest covers
Leaving palm rest covers or other material on the palm rest surface of your computer could result in damage to the display when you close it.
To enable thin design, the clearance between the display and the palm rest area is engineered to tight tolerances. Do not use palm rest covers as the added thickness may interfere with the designed resting position of the display.
As a best practice, keep the palm rest clear of any material.