If I could see the weights, in my order history, I could do a reasonable comparison
of shipping rates between the sellers I have purchased from.
If I could see the weight on the invoice, I could more easily determine if shipping
was in line with expectations.
I did in one case message a seller to ask the weight, and the shipping was completely
in line, I had just not realized the weight was as much as it was.
When adding to an existing order, I can only see the weight of what is in my
current cart.
If I could also see the weight of what was already in the order, this would be
very very useful.