Can Cause Fear: This unit frightens all enemy units, reducing their leadership when nearby. It is also immune to fear. Fear penalties do not stack.
Hide (forest): This unit can hide in forests until enemy units get too close.
Undead: The unit is Undead (does not rout, immune to terror, becomes unstable when is low).
The Tithe (Zombies) is a Vampire Counts melee infantry unit. Zombies: shuffling, mindless, ambling towards their foes - on an unending quest for flesh.
Zombies are shambling horrors that stagger towards the enemy battle lines in a noisome horde. Grotesquely reanimated corpses, they are compelled by the Dark Magic of a Vampire or Necromancer, and driven by the will of their master to commit acts of extreme violence. To call the way a Zombie attacks "fighting", is perhaps to give the foul creature credit beyond its due. These sickening half-things have no skill to speak of, but are instead driven only by the insatiable urge to rend, kill and consume the living. Any warrior unfortunate enough to be pulled down by a Zombie horde will find himself torn slowly apart by a mass of desperate clawing fingers, his flesh gouged from his body in grisly, glistening chunks. The fortunate die quickly, but those unlucky souls who are trampled beneath the horde spend their death throes in miserable agony as their innards become a crimson feast.
↑Meat Shield: While unimpressive at causing damage, this unit is useful as a 'meat shield', absorbing damage that would otherwise hurt a more useful or precious target.
Gaining 30 unit models, 4 melee defence, 2 melee attack, and 15% physical resist, the tithe is a way of streamlining your fodder space down at the expense of overall value. With more models and physical resistance, they can be a more durable roadblock. Not factoring in the differences in melee attack and defence, the unit is approximately 40% tankier (as a result of both its additional unit size and physical damage resist) than a regular unit of zombies; but for double the cost.
In any situation where you could instead take two units of zombies, you will likely do better by doing so. If you, however, only have the space to take a single unit of fodder then this unit will, very roughly, perform nearly as well as two units of zombies.