This anti-aliasing mode removes the jaggies (aliasing) during the screen representation, as the edges of the objects are smoothed.
The anti-aliasing mode makes the screen redraw slower.
The anti-aliasing mode is automatically switched off in the zoom levels higher than 16x.
The screen redrawing in anti-aliasing and spot color mode is quite slow if the map has a lot of objects or big raster background maps are loaded. In this case we recommand to switch off anit aliasing.
Read more about Anti-Aliasing in [Wikipedia].