Basically it is about using a heavier GCR ratio, swapping more K for less CMY, obviously this has both pros and cons.
A free ink density inspection utility for Mac/Win here:
<http://www.tglc.com/english/PerfX/image_ink_saving.html>
Ink reduction is often applied as a DLP back end solution at the RIP, where the GCR of incoming CMYK data (raster and vector) is adjusted to something that the printer prefers - as opposed to what the separator supplied (often without any notice to their customers, whether they wish it or not).
<http://www.tglc.com/english/PerfX/ICC_DeviceLink.html>
<http://www.fineeyecolor.com/icesaver.html>
Regards,
Stephen Marsh