How can earth bags be "too big for the job"?

Besides the actual weight and the act of lifting them up to put on the wall, I have read a number of posts saying that bags that are too big are "excessive" or use too much material. To my way of thinking, if the bag is twice as big, it will take about half as many bags to do the job (yes, I know, they will be much heavier). It will also provide more thermal mass for the building, which may or may not be good. What am I missing?

Tom, there is much to this type of building...

Perhaps get some bags and experiment, while reading one of the books, or take a workshop. You will learn a great deal.

You do not lift bags...you lift material and put in the bags. Some jobs don't employ bags, but tubes...and...you fill the tubes as you build the wall...

I've never heard that about earthbags but I have heard it about tires as in earthships. 4-5 wheelbarrows full to fill one tire. The poly bags can be found in many sizes. The 25 lb rice bags seem to be the most commonly used.

http://www.earthbagbuilding.com/

The above site has about as much info as you can get in one place online for earthbag building including videos and pics. Spend the rest of the day there and you'll have a good understanding of the system.

When/if you decide it's for you, the book earthbag building and techniques by Kaki Hunter and Donald ________ was written as a how to manual and the goal was to make things as smooth and easy as possible. They went through the process slowly and figured out solutions to any difficulties they encountered.

Hey Tom,
I'm gonna assume that you might have read people discussing the appropriateness of 100lb bags, wherein most designs appropriately utilize 50lb bags (rice weight, not earthen fill weight). It's the width of a 100lb bag that is overkill most of the time, but all in all they are premade flexible forms for rammed earth, and each situation calls for their own parameters. I like the 50lb'er, especially when filing with loose fill light weight pumice/Scoria up scaffold/ladders. For straight walls of rammed earth I usually set up slip forms spaced at the 50lb bag width.
Earthbag Chris