One of the chief benefits of waterjet cutting machine over thermal cutting processes is that there is no heat affected zone created. A heat affected zone is a concern when the design of an application is concerned with the properties of the metal being cut, as is the case with thermal cutting processes. Furthermore, waterjet cutting machine can be used by any material ranging from plastic to steel and does not produce smoke.
Waterjet CNC machines can also deliver great precision and fine-tuned control. They reduce the amount of scrap material produced as a by-product of cutting, and allow cuts to be placed closer together.
article from: http://waterjetapw.com