The Resize / Draw Indicator option allows you to toggle on or off lines which appear from the top to bottom of the grid as an indicator to assist in the movement or resizing of effects.
To enable or disable the Indicator lines, click the Resize / Draw Indicator item on the Edit menu, you can set the color of the lines in the sub menu of that item.
When enabled, the indicator line will appear at the beginning or end of an effect when you resize that effect. If you are moving an effect, the indicator lines will appear at both ends of the effect.
The indicator lines also appear for the Draw Box when using the Draw Mode feature.