What is a GSU or DGS number and should I care?

I was recently asked about this and thought it would be good to share in case others had similar questions as they looked at sources and citations for their ancestors.

I spend my days trying to think of ways to make searching for names dates and places easier for just about anybody who wants to do Family History Work. I have found that what is easy for a 14 year old and what is easy for a 65 year old are not always the same.