I have a customer who wants to have the weight of a purchased amount of an item deducted from the inventory. For instance. She sells Rice. She enters that she has 10 pounds (160 Ounces) of rice in the "amount of product in stock" on the details tab. She has attribute/options for 1 pound (16 oz), 1/2 pound (8 oz), and 1/4 pound (4 oz). and prices and weight for each in the attribute.
If a customer buys 1/2 pound of rice, she wants that deducted from the inventory. The problem is that if she puts the attribute dependent to be able to enter a weight .... she also needs to put "amount of product in stock" in each attribute, which would not be desirable because you just don't know how much someone will want from the whole amount of the product.
If she makes the attribute independent then she can not enter the weight for each attribute and the inventory would be updated to deduct 1 in the weight designated which is ounces only, not for the other options she wants to provide.