Quoting mqpiffle, reply 3I believe it is purely a cosmetic feature
I wish it were purely cosmetic, but my armies are still dodging around them, being forced to leave the road.
I think to me personally I feel this is a problem with the pathing, when multiple armies can (sometimes) figure out how to move ontop of eachother, why don't they when moving around randomly? 
sincerely
~ Kongdej