You can easily sort your stuff, like Herbs.
Holding "ALT" and clicking on the item stacks all items of the same type into one pile.
Their qualities will be combined and an average of all will be the stack's quality.
You can move items from one opened inventory to another open Inventory.
Holding "CTRL" and clicking on the item will move it to the other inventory.
You can split a stack of Items.
Holding "SHIFT" and clicking on the stack will open the stack split dialogue.