So you spend 5 minutes getting 250 branches from a tree next to a stock bin and a row of kilns. you then put branches into the stock bin. then take branches from stock bin and fill the kilns. then refill the stock bin.
I pick 250 branches fill kilns and i'm done. I would still find it much easier to fill the kilns therefore making them the stock bins saving me another step. I can not even really see much of an efficiency value if at all.
On the other hand back to the dross argument it takes 45 min to get dross. and your miner is probably not your farmer let alone needing that dross on the field at that time. So stock bins for things like dross makes scenes. Stock bins for projects that need several hundred to do make sense such as paving materials and wall mats. There has to be a line drawn for what stock bins are used for otherwise you would not build anything but a stock bin.