Master is basically used for specifying which renderer will be used by the commandline render calls. There's certainly no difference in quality when Master is checked.
In fact, there's a bit of misunderstanding about the renderer presets in general in the default scene I think, which is that people think there is some actual qualitative difference between Quick Render and Full Render, but there isn't. If you set the Quick Render settings to the same as the Full Render, the results should be essentially identical (I say "essentially" because there are sometimes slight variations from render-to-render, due to variations in random number generation).
- Oshyan