Both designers will work on the functionality of an object only from a different perspective. And both have influence on the looks of the final product. For example: An environment friendly technique can be very dominant for the looks. (Think of lasercutting instead of silkscreen printing)
I made a scheme that shows which ingredients a product needs. This can be a start if the product-idea (which product are we going to make) is already there. The questions mentioned are just a few examples to show the differences in approach.