The DRAW_NONE drawing style is used in cases, when you need to calculate and show the values of the indicator in "Data Window", but the plotting isn't needed. This is example of the indicator, that shows bars index in the "Data Window".
The bar indexing is set as timeseries, it means that current uncompleted bar has index=0, the oldest bar has the highest index. Note that the indicator doesn't plot anything (DRAW_NONE), despite the fact that red color for the first graphic plot is defined.
See also: The Drawing Styles in MQL5.