What exacly is the purpose of a CSM in a deployment aside from trying to bring a garrison atmosphere to the battlefield?

And the Chief goes there!

Here I thought the CSM 's job in country was to keep the reflective belt gods satisfied. (Just kidding)

Actually a question I've thought about many times. I believe it depends on the quality of the CSM. I honestly believe that there are more CSM slots than there are CSM quality troops.
That being said, I'll relate a couple experiences I had in country. A sergeant in my company was recommended for art 15 by his platoon sergeant (in my opinion extremely unfair and ridiculous.) CSM calls him into his office, asks the sergeant for his side of the story. CSM holds the paperwork over the garbage can and rips it into pieces.
The day I was pinned to SGT, my first sergeant invited me to eat chow with him, the company commander and the same CSM. CSM asks me how long I'd it had taken me to make SGT. I told him. He replied that I hadn't been in long enough for the responsibility, and that I'd better learn fast. He talked about leadership for a while, then talked about what was wrong with the Army and NG, and the kind of leaders needed. He was able to tell me that I wasn't ready to be a sergeant without belittling me, and while giving me advice on how to do the job well.
Just a couple reasons why we have CSMs in country.

The CSM is the one charged with keeping the morale of the troops up and advising the command structure as to the needs of the enlisted troops...