Equal consumption of all the miners on an ore patch. The opposite ore loading, unloading at an equal rate so trains spend the minimum at a station (probably the more critical part to balance since you can solve the input side with buffering). Taking multiple less than full lines down to fewer full lines in a way that is evenly distributed, either to conserve space or, in larger bases, UPS. On Fulgora, with uneven recycler load, balancing the flow of an unfiltered belt before you separate it. Those are examples I just pulled from my current play through but I could probably find more.