Moving average is a great tool to identify the asset direction. However, it's hard to see whether the moving average speeds up or slows down from just looking at it. Ideally we want it to go faster as it will show a strong trend. And if it slows down - then the trend becomes weaker. This indicator helps to identify it. Theoretically, it could be shown with an angle of the moving average, but I don't like this idea as the angle depends on the scale: you zoom in and it looks very steep, you zoom out - and it's all flat. But the percentage change is always the percentage, no matter what zoom you use.
It also allows you to set a twilight zone to filter periods when MA does nothing.
Think about this indicator from this perspective: if a normal moving average shows the speed of a trend, then this indicator shows the change of the speed or in other words - acceleration.