Wood finishes are usually thinner than standard decorative paints and you may wish to spray a small volume, say half a litre. Airless can spray gloss and varnishes very well, especially if you use a Fine Finish spray tip, but the system needs at least 2 litres of paint to fill it, so you can use an HVLP spray gun powered by air from a portable turbine, for small volumes of material.
In a factory situation, say spray painting furniture, you may need to spray a heavier, tougher material, which could be too heavy for a simple HVLP spray gun.
To retain the superior atomisation of an HVLP gun but be able to handle the heavier materials, you need to help the spray gun by supplying the paint under pressure; also you will probably require a larger volume of paint to be available on a production line, without having to stop to refill a paint cup. As most factories have plenty of compressed air, air assisted airless is the usual equipment, with the compressed air driving a pneumatic pump or a pressure tank to feed the paint to the gun, and a second air line to power the gun.
