CAD for plumbing, what is it, and its capabilities?

I have a good idea what a CAD is ( computer animated design? ), but what does it do plumbing wise? My mom said she would like me to do bids for there plumbing company and mentioned the CAD system. They dont have one and I was interested in it to expand the business capabilty / speed. Details on what it does, and what its benifits are.