Video Scope Question

When the timeline plays the scopes drop resolution because they take system resources to play in real time.
RGB is useful for white balancing by eye and sometimes easier for keeping levels legal. Sometimes your levels will look fine in the Waveform but in the RGB Parade you'll see one color clipping. You can see that when you look at the Blue channel in my RGB where it's below 0 compared to the Waveform.

If you want to see really nice scopes you should see what they look like in FCPX.