If the value is set to 100%, the quantizer will stay nearly constant (high motion scenes will look bad). If it's 0%, the quantizer will be changed to make all frames approximately equally sized (low motion scenes will look bad).
Quantizer blur
Blurs the quantizer graph over time: 0% - no blur, 100% - average all past quantizers.
Max quantizer difference
Limits the maximum quantizer difference between frames.