Object Oriented Programming principles require classes to be dedicated for one and only one aim, to have a very isolated purpose. And there is a quote from MSDN http://bit.ly/sLMxHy :
In longer code files, it is convenient to be able to collapse or hide one or more regions so that you can focus on the part of the file that you are currently working on.
If we put these two statements together, the conclusion will be: “Regions in Visual Studio are to support violation of OOP principles”