A view of the 15-inch MacBook Retina Pro (Photo Credit: Apple.com/screenshot)
With the title, "Do not use palm rest covers," it seems simple what the warning was.
According to Apple the reason not to use the palm, or wrist, rest covers on the surface of the computer could result in damage of the display when the MacBook is closed.
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Apple's resolution to the matter, "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."
They added to have the palm rest surface clear of any material.
Palm rest covers are used to avoid scratches, stains, or similar damage to the area. It can also be used to personalize the laptop.
According to Wise Geek, there might also be a heath concern when it comes to the palm rests.
It noted, "One school of thought suggests that wrist rests do help align the user's hands and wrists while typing or mousing, while another suggests that they may encourage users to relax their hand positions too much while typing. Instead of decreasing the number and severity of carpal tunnel injuries, an improperly used rest may actually cause more repetitive stress injuries (RSI) for those who type or mouse for extended periods of time."
They added that a wrist rest, especially a gel-filled type, is a better choice than no support at all. Wise Geek stated the unsupported wrists and lower hand can experience fatigue and may fall below the level of the keyboard, "which is an especially dangerous positive for repetitive typing."