The viewport renderer can do various amounts of shadowmap sampling to produce a higher quality result.
Area lights are treated as point lights when generating and sampling shadow maps. This is the fastest option.
Do some antialiasing of shadow edges. Treat area lights as point lights when generating and sampling shadow maps.
Area lights generate multiple shadow maps which are sampled to generate an approximation of a blurred shadow from an area source.
Area lights generate multiple maps and antialias the shadow lookups.