7. The Menus / 7.2 The Edit Menu
This command allows to turn antialiasing quickly on and off. Antialiasing means, that the edges of text and vector graphics are drawn unsharp by creating interpolated colors. Usually this looks nicer.
If you want to use images in the web, this is often not desired. In this case the files should be as small as possible, but this is possibly prevented by antialiasing, because it increases the number of colors used.