When presenting five cards as four, it is used to hide the third card from the top.
When presenting six cards as four, it is used to hide the third and fourth cards from the top.
Tutorial
See:
Card College, Vol 3
Cannibal Kings by Lin Searles presented by Michael Ammar
Easy to Master Card Miracles Vol 1
Daryl - Encyclopedia of Card Sleights, Vol 7
Used in:
Cannibal Kings