An op-ed in today's Daily Journal by six former jury foremen is instructive.  Let's keep it handy by posting a bit of it and the link here.

The grand jury analyzes whether a government agency is operating in a businesslike manner and providing public services effectively and economically. The grand jury seeks to identify and interview individuals with expert knowledge and diverse views. There would be a chilling impact without the guarantee of confidentiality. The grand jury typically provides its data to the government agency being investigated prior to publishing a report to ensure errors have not been made. Also, every proposed report is reviewed in detail and must be formally approved by at least 12 of 19 jurors.

The piece as a whole sounds authoritative and pretty complete and more "businesslike manners" would certainly be welcome.