"Change image on mouse hover" — the feature is implemented and used when you need to display over one product image on your collection page. You can use the task if you want to display both back and front images of a product. 

When you hover the mouse over a product image, the feature will display the second image that you uploaded for that particular product. And when you hover the mouse away from the product image, the image will alter back to what it was in the first place.