That wording is a little confusing I think.
When the motor signal is set to Neutral, the motors spin at the speed you set up for "lowest reliable speed" when you did the wizard. Checking that check box will make them spin at that speed when the throttle stick is all the way down. That is what this means.
The default for LP flight modes is to stop the motors if you move the throttle stick all the way down. That is a safety feature.
Some people want to do flips with their quad, and they want the motors to continue to work even if they move the throttle stick all the way down, so they can still control it, even with the throttle stick all the way down. This is one way to slow the motors down, but not stop them during flips. CruiseControl is another way, but it works differently...