Here are some of the benefits to using a waterjet:

• Cheaper than other processes.
• Cut virtually any material:
  • pre hardened steel
  • mild steel
  • exotics like Titanium, Inconel, Hastalloy
  • gummy 304 stainless
  • (most steels cut at the same speed, whether hardened, or not.)
  • Copper, Brass, Aluminum: They are a cinch!
  • brittle materials like glass, ceramic, quartz, stone.
  • laminates
  • flammable materials
• Cut thin stuff, or thick stuff
• Make all sorts of shapes with only one tool.
• Cut wide range of thickness’ to reasonable tolerance up to 2” (50mm) thick
• Up to 5” (127mm) or thicker where tolerance not important, or in soft materials.
• No Heat Generated / No heat affected zones - this is cold cutting!
• No mechanical stresses
• Cut virtually any shape:  
• Fast turn around on the machine.  Make a part, then 2 minutes be making a completely different part from a completely different material.
• Leaves a satin smooth finish, thus reducing secondary operations
• Clean cutting process without gasses or oils
• Narrow kerf removes only a small amount of material.
• Modern systems are now very easy to learn.
• Can easily switch between high production, and single piece production, on the same machine, with no extra effort.
• Are very safe.  (No, they don't explode, thanks to the nearly incompressible property of water.)
• No "scaley" edges, which makes it easier to make a high quality weld
• Machine composite materials, or materials where dissimilar materials are glued together
• Machine stacks of thin parts all at once.