|Or 'her part'. Sorry ladies!|
It's a little ironic that when a Legion finally manages to get ATSKNF after years of complaining that they don't have it, suddenly apparently nobody wants it. But I digress.
Now we all know that if you're playing an MSU force, Morale is very much less of an issue in 8th Edition. If there's only five of you and you're LD 7, by the time you take enough damage to be in danger of failing a Morale test you're practically all dead anyway. But what I think people aren't giving due consideration to is the fact that in 8th Edition in particular, Cultists are really, really useful. They're one of the cheapest ways any Faction can fill the three Troop slots needed to fill out a Battalion, and whilst nobody is going to accuse them of being the most deadly troops in the galaxy with the various buffs and re-rolls available to Chaos they can be surprisingly effective.
It's worth re-stating how useful filling Troops slots with Cultists can be. For one thing they get the Despoilers of the Galaxy rule, the new version of Objective Secured with all the utility that entails, but most importantly the Battalion (or even Brigade, if you really want to push it) detachment is in reach, giving you +3 or more Command Points. These were very useful just with the Indexes, but with a full Codex they become significantly more important. The thing which is increasingly becoming clear is that most of the benefits that used to come with Formations now come as Stratagems, so a healthy pool of CP greatly increases the flexibility of your army. World Eaters, for example, have the very powerful Fury of Khorne to allow a unit to fight again- potentially for the third time if it's a unit of Berserkers- but it costs a full 3 points. Not only will filling out a Battalion get you the points to use it, but it means you can have a few units of cheap autogun-toting idiots holding the objective so all those Berserkers can get on with running at the enemy with chain-axes.
Even the mighty Land Raider can gain a decent benefit from Cultists. Though the tank has got a lot more powerful in 8th, (particularly the Chaos variety since it gained POTMS) its Achilles Heel is getting assaulted by quick, cheap units like suicidal Rhinos and Trukks which stop it shooting. Well, Cultists not only give you a cheap bubble-wrap option but you can even load a smaller unit of them into the thing and take them with you. Even if you misjudge it and still get charged, you can hop the Cultists out, retreat the tank, and charge the Cultists in, at least preventing the Rhino from doing it again next turn.
Lets finish by really looking at just how nasty we can make some Cultists. We need to remember that, chaff unit though they are, Cultists still get the HERETIC ASTARTES, <MARK OF CHAOS> and <LEGION> keywords, so as well as that Morale re-roll we started talking about we can get always-strikes-first Cultists, Cultists with additional attacks, and more. It's probably easiest to make them into an assault horde, with a Dark Apostle keeping them in the fight and dishing out melee Hit re-rolls with Dark Zealotry and an Exalted Champion giving them re-rolls to Wound. On a 20 strong unit that cost 5 Power, that's some force multiplication. If there's a Sorcerer about, Prescience will give them +1 To Hit into the bargain. And whilst Chaos doesn't have Commissars to boost the staying power of Cultists to Conscript-like levels of irritating, the Word Bearers have a potentially even more infuriating trick, with Tide of Traitors (for a measly 2CP) allowing them to remove that one survivor stuck in melee with an enemy unit (who maybe only stuck around because of that Ld 9 and morale re-roll) and replace him, along with his full twenty-strong unit, on your opponent's board edge in rapid-fire range of his tender bits.
Of course, you don't have to take Cultists. There's plenty of perfectly good army builds that don't need them. But there are plenty of really dirty jobs to do on the 40k battlefield, and like Grots and Conscripts, Cultists are one of the best units to saddle with doing them.