By default in our product table quantity is 1 and when you add the product into the cart product quantity will back to 1. If you want to set product quantity 0 instead of 1, you can easily do it by using a filter hook called wpto_qty_return_zero.
Now suppose you are using one of the quantity control plugin. In that case, when you add a product to the cart, the quantity will back to the minimum value.
But you want that quantity should be the same increment value. For example, your product minimum quantity is 2 and you increase value to 6 and then add the product to cart. Now you don't want that the quantity value set back to the minimum value 2. You want quantity value remains that increase value 6.
For that we just need to use 'wpto_qty_return_quanity' filter.