So, currently if you have a Spice Rack or Elemental Pouch, and you make/find/extract more of an item, it stacks into the pouch. But not if you have a generic pouch.
I realized I spent a LOT of time stacking things on my own. I basically had a "Tool" pouch, a "Food Ingredients" pouch, and a "Food/Drink" pouch. But if I had, for example, 6 wheat in a pouch and I got more - it shows up outside of the pouch. This fills an empty slot, and I have to end up dragging it to the right pouch (sometimes blindly) and stacking it manually.
This was a rather annoying task, as having Cherries and Bubbles in a pouch made it really easy to fill up 4 slots at a time. And at one point I accidently had wheat in 2 pouches without realizing, and picked up another. So that's 3 slots for 3 of the same item that stacks easily.
As said in chat, there was the idea for a "Not Having Your Eggs In One Basket" badge. But really, I don't see why this "feature" exists. If it's not crucial to the mechanics to have autostacking on everything, then why not? Saves lots of time.