In previous editions of Warhammer Fantasy (and indeed in many wargames) there was the concept of 'chaff', a small unit that have very little combat ability and are generally included in a list just to get in the way of opposing units and die. Typically used to block movement or force overruns in unfavorable directions. Ideally very cheap in points cost and the more maneuverable the better. It's derived from the concept of the inedible stem of a grain crop: to separate the wheat from the chaff is an old concept about finding good in a pile of rubbish for example, and has also been historically referred to as anything aircraft drop to confuse radar detection. Either interpretation works in this setting, as chaff has traditionally been used in Warhammer to cause target priority problems, interfere with lines of sight, firing or charge lanes, and provide some kind of cheap tarpit to hold up the enemy while the better units in your force do the trick. Let's check out how to best make use of chaff in AoS, and be sure to check out our other tactics articles as well by clicking here.
In AoS
Now that there are no points in Warhammer: Age of Sigmar, some seem to believe that the time of chaff has passed us by and we no longer have use for these weak misdirection units, but I disagree strongly. If you're playing with a points-derived comp system such as SDK or Pool (both of which can have lists written in this excellent tool on http://www.scrollbuilder.com/) then there certainly still exist value disparities between units and you can take grots or gnoblars without as much pain from your list. However, I still believe there is value to your chaff even if you are using wound counts as a balancing factor or sticking to the core rules and using model count alone.
Chaff can still work as a tarpit if you use it in the old fashion (a deep unit of skaven slaves, for example) but you can also change things a bit in Age of Sigmar to make use of the new rules. An optimal chaff unit in this new ruleset seems to look like a big wall of bodies, perhaps spread thin and wide. arranging like a net, the opponent loses the ability to move around them. In AoS, you cannot come within 3 inches of an enemy model in the movement phase so a relatively small unit in a broad arrangement effectively blocks the movement of anything that can't fly, and almost forces a charge out of the unit if it wants to move past your screen.

If you have a set of wizards or a cannon tossing out big damage and need to keep them defended, chaff is still a really useful tool even without a comp system, as long as you can play it right. As we see new battlescrolls emerge and new battleplan scenarios unveiled, we may find yet even more reasons to love and use chaff in our games, and I'm excited for the new tactical possibilities that will accompany it.
How have you found chaff to fare in Age of Sigmar? Do you have any tips to share or other tactics you have explored? Let us know!