product images vs detailed images
 

I just noticed that if we do not upload product images and upload thumbnail and detailed images and then consider that if the thumbnail is clicked, this takes to the product details page and displays the image of the detailed image. When now the mouse is hovered over the product image, the zoom image pops up in a different image window. Consider this http://www.indiancarnival.com/HANDWOVEN-DESIGNER-SAREEE.html

This means that product image is not important to be uploaded. So, if i do not upload this, what effects will it have from the customer's end?
Also, I guess, this will save space on the server too. When is the product image required to be uploaded?

Re: product images vs detailed images
 

The product image is not required. If you do not have a detailed image, and you want to show a larger image on the product page, then you can upload the product image.