The role of the mastering engineer within the production process.

The role of the mastering engineer within the production process. Discuss the history and changing environments in this regard in relation to current practices. Back this up with appropriate sources and critically evaluate.
Or
CD Mastering Processing Chain why is analogue still so popular? Discuss the history of processing for digital (CD) mastering and the pros and cons of analogue hardware vs digital hardware and plug-ins. Support this with appropriate sources and critically evaluate.