Waste of Transportation
See link to Assembly Mag article: AGV vs. Conveyor.
This is a good, short article, outlining the pros and cons of each system. But, in the context of lean, which this aritcle was presented as...it misses the point. Well, one thing was true about this article, there is "no right answer" when it comes to choosing how to move material in your plant.
But, whether you pick AGV, conveyors, fork trucks or whatever...the main goal is to eliminate moves or minimize to the best of your ability.
Someday, I'm going to invent industrial levitation...