Pyramid is aliased on left, antialiased on right.
Antialiasing smoothes the staircase effect that occurs when diagonal or curved lines or borders are drawn on raster displays consisting of square or rectangular pixels. Antialiasing can be either on or off. Turn this off only when you're rendering test images and want greater speed. Leave it on at all other times.
You can also turn antialiasing off for the sample slots to speed up redraw of the sample objects. Click the Options button in the Material Editor and turn on the Antialias toggle on the Material Editor Options dialog. Default=off.