Until recently it was impossible to create 3D printed parts from copper but that has since changed and Proto Labs is launching a copper 3D printing service using Direct Metal Laser Sintering (DMLS) technology.
If you want a part with complex geometry, such as intricate internal channels or a honeycomb structure to save weight, then you are no longer constrained by the production technology available to you. For prototyping it means you can test a concept and quickly reiterate it to ensure that you end up with the optimum design.
Proto Labs uses use CuNi2SiCr, which is a low-alloy copper. It combines the electric and thermal conductivity that you want with good mechanical properties and corrosion resistance, so you can develop parts for harsh environments where using pure copper is not feasible.
Of course, Proto Labs can also produce copper parts using CNC machining, which might still be a better option if you need higher volumes or parts with a simple geometry. It really depends on the application; Proto Labs offers both manufacturing processes. Go to www.protolabs.co.uk for more information.