This is a unit in the Warhammer 40K Chaos Space Marines Codex that is often overlooked. I mean really, it’s only 2 points cheaper then a basic Chaos Marine and has the same statline, but gives up it’s armor, weapons, and wargear to get a 5+ invulnerable, Fearless, and a quasi-deep-strike off icons.
So, it’s more fragile against most stuff it’s likely to fight. And it has trouble assaulting into cover due to a lack of grenades and a weak save. What’s it good for? Tactical Reinforcements.
Essentially, these little guys are good for popping up where you need a little extra help. They can assault the turn they arrive, so they con pop down and join an on-going assault, or tie up a nearby enemy unit that stinks in melee (hi guardsmen, how are you today?), or they can also be a cheap scoring unit to leave sitting on an objective twiddling their thumbs instead of wasting one of your pricey killy units on that job.
For example, Plague Marines are often looked to for holding an objective. But even a small squad is very expensive. And if they sit on the home objective all game while the rest of the army goes after the enemy, they usually just sit there being an expensive paper weight. Lesser Daemons can fill that same job for much cheaper.
They can also throw enemy plans off. 1 scoring unit moves near 2 objectives and the enemy commits to trying to contest the 1 the unit could likely reach. Suddenly there’s a second scoring unit and not enough enemy forces to stop them both.
Now, not every army has equal use for these things. A highly mobile army with lots of bikes, transports, raptors, etc, probably has the speed to change up the battle plan as needed. Less mechanized forces can find the extra flexibility of bringing them in quite desirable.
And that’s ultimately what lesser daemons offer. Tactical flexibility. Anytime you can reliably place a unit where it needs to be after the battle has already started shaping up, that gives you an advantage. They’re a bit on the weak side, but for the price, they’re worth it.