Anti-aliasing smooths all objects displayed that results in smoother edges, less ragged lines, more realistic intersections. However, this function is very costly and the quality highly depends on the graphic hardware.
Note, that anti-aliased scene cannot be manipulated (rotated, zoomed etc) therefore a built in mechanism called quality auto scaling, unique to MarvinSpace, automatically turns off anti-aliasing for moving images and turned it back when image is standing still.