If I want my materials to be used in production or be offered to other people, I put them in the raw warehouse.
If I want my materials to be sold in the shops, I put them at the product warehouse.
I want another warehouse, that will be used to stock products. The raw warehouse doesn't fit this properly. Imagine I have a high QL raw but I don't use this to make high QL product. Instead, I use it to make low QL product. Would it be smarter if I use this high QL raw to sell to players and buy low QL raw to my production. The system as it is now mix all raw together and I can't do this properly.
Another warehouse would make it good. Make it use the capacity of raw materials and not count in the building max number.