Relic Units

The purpose of the relic requirement is to allow the opponent to deny you access to certain units if certain portions of the map are lost, encouraging map control and denial for strategic purposes. This also allows unusual asymmetries in the matchup to be strategically created by holding different portions of the map, for instance by one player holding both relics while the other player holds other things.

The gameplay effect varies by race. Usually relic requirements:
 * Make a race more vulnerable to certain special weapons, such as plasmaguns, due to reduced access to vital armour types.
 * Make it harder for a race to deal with certain armour types, when access to vital weapons are lost.
 * Introduce a risk when making a fast tier from Tier 2 to Tier 3 with the aim of surprising an enemy with advanced units.
 * Subtly makes the race more vulnerable to lategame Infiltrators as:
 * Relic uber units tend to be detectors.
 * An inability to access hero wargear means potentially you cannot get the wargear that improves the primary commander's ability to detect infiltrated units).

Relic Units

 * Relic squads tend to be Tier 2.5, with exceptions.
 * It is not necessary to have Relic squads available earlier in the game, as Relic denial causes an inability to purchase new hero wargear that are typically available from Tier 1.

Chaos

 * As chaos units do not scale well in ranged damage the loss of Obliterators chaos to lose a major source of ranged damage, making them shift to a more melee-centric army.
 * Obliterators are a key source of the Daemonic armour type.

Space Marines
Elite Heavy Infantry take reduced damage from plasmaguns by about 33% when you compare it to tactical space marines armour.
 * Space marines are the only faction with 2 relic squads.
 * Terminator and Assault Terminators are their main source of Elite Heavy Infantry armour type. Relic denial makes the Astartes more vulnerable to plasmaguns. To mitigate such weapons they would have to use Grey knights, Vehicles or Scouts.

Orks

 * Mega Armoured Nobz and Squiggoth are two of the Ork's main late game base bashing units.
 * Mega Armoured Nobz are Ork's only source of Elite Heavy Infantry armour. This makes them one of the best ways to destroy Heavy Bolter-equipped units.
 * Squiggoth is one of the best ways to destroy groups of Walkers (such as Defilers). Other Ork anti-tank units have trouble doing so.

Eldar

 * The Seer Council provides a source of significant disruption to gunlines.
 * When equipped with upgraded Witchblades, the Seer Council is one of Eldar's best ways of destroying light structures.
 * The Seer Council reduces the cooldown of the Farseer psyker powers. Denying Eldar access to the Relic effectively reduces Eldar's ability to bombard you with psyker powers.

Imperial Guard
Losing access to the assassin for IG significantly reduces:
 * Their ability to kill heroes.
 * Their line of sight over the map, as the Assassin has tremendous line of sight. Instead they have to rely on forward scouting which is no where near as good.

Tau

 * A Tau player who focuses on Mont'ka is impacted differently than one who focuses on Kauyon.
 * Crisis Suits are one of their best ways of dealing with Daemons.
 * Tau seem less impacted by it, which fits with the theme that the Tau way of war is less concerned about taking and holding terrain.

Necrons

 * Pariahs can reinforce outside of the Necron zone of control (where other Necron units cannot). Thus it impacts their map presence.
 * Restored monolith provides a moving zone of control. Thus further impacting their map presence.

Dark Eldar

 * Warpbeasts are a key source of the Daemonic armour type.