Poop pass right through? I haven't found that to be the case, and I have bantams with droppings smaller than standard size chickens. I have found that a fair amount of droppings get caught on the wire, and then you have to scrape/clean the wire, which to me is a very tedious job. And of course wire isn't easy on a chicken's feet, so you wouldn't want the bottom of your coop to be composed only of wire anyway.
I like plastic boot trays under the roost. They're light and you can take them over to your composter, dump out the contents, and hose them down. Then when you replace them they're clean as a whistle.
One other issue with wire bottoms is predation. If the openings in the wire are larger than 1/2" by 1/2", you risk having some critter grab at your chickens through the wire. I've also read about birds having their feet bitten off through wire bottom cages.
