I'm aware of this, and it is a useful feature in its own right, but it doesn't address the reasons for what I describe above. For instance, you have say, 967 biofuel in total and you have 7 generators. So you want seven evenly sized stacks of biofuel to put in each generator. With the functionality I describe above, you just clear some space in your inventory if necessary, pick up each stack, drag it over the same seven slots. EASY! :)

Using the current right click functionality, it is much more awkward to do. First, you have to divide 967 by 7! Rounded down that is 138. So you split to 138, but then you're left with some stacks of 62. Put them together for 124. Argh now you have to split the rest to bits of.... you see?

WIth drag and drop, it's easy to get what you want.