If you teleport into a corner of ceiling (no matter if the ceiling is higher or lower than your character), the corner pushed the character a few pixels away. The push distance is based on how far you are from the edge of the corner. One corner boost can save 1-3 frames; and while this isn't very significant in full-game runs, during the game you can execute several of them, saving a total of 20-30 frames (0.333-0.500 second) if you do them successfully.

Here is a demonstration of a corner boost in slow motion: