PLA is a biodegradable thermoplastic that has been derived from renewable resources like corn starch and sugar cane. This makes PLA environmentally friendly and very safe to work with. PLA also has a very sharp glass transition point so if you use a fan to cool it, it will set into a solid very quickly.
PLA can achieve a greater range of geometries than are possible with other plastics. It also reduces the thermal stress on the printed part, making warping less of an issue with larger PLA parts. PLA can also be painted over with acrylic paint.