After a while that oil will begin to saturate the screen and from the heat of the macbook once you close the lid, it will adhere through a bonding process that is extremely difficult to remove without technical and clinical processes.
Has this happened with you or with anyone you know?
But this will only happen if there's a lot of pressure on the top or bottom of the laptop
----------
Get a Moshi keyboard cover and use that while you are using the computer. Once you are done, remove the keyboard cover. Residue oil from fingers problem solved.
Instead of that shall I just try cleaning it everytime?
Also shall I get a case like the speck ones to enlargen the gap between the keyboard and screen