Year End and Data

Hello, 

I have been searching for and can't seem to find the information that I am looking for. My question is, what exactly does Year End Processing do to the data inside of SAGE? Does this make it so that fields can no longer be changed in that fiscal year, that no new transactions can be entered, etc? Any information or a link to information on this would be a big help. Everything I have found so far is on HOW to perform year end processing, but not what this actually does to the data.

Thanks!