Many players and guilds are underestimating raid buffs and debuffs, players there don't like to run buff-specs or they are slacking on buffs uptime. So just to make this Wildstar mechanics more clear, I will accessibly explain it here. No hard math or nitpikcing, only short and simple explanation for everyone to understand the importance of buffs and importance of their uptimes. And if you are the player on buffs, remember - you are very important to raid and your death will be a really big loss.
At first lets check the "weakest" buff - EMP or Empowering Probes from Medics (+5% to damage and +5% to healing). And just by looking at it we can see that 5% is 1/20, or one from twenty, and in raid there are twenty players, so it is 1/20 twenty times, or it will be 1 whole player. So bringing up the weakest buff is already like raiding with 21 instead of 20. And other buffs are giving even more - Bloodthirst is giving 8%, Powerlink is giving 8% and Armor Shred in addition. Void Pact is giving 12% Assault and Support power - so your tanks with it would have stronger defensive cooldowns, your heals and DPS would have better output as well. Those buffs are like 1.5-2.5 more players in raid each, and when they are buffing each other it will give even more in total. Having all buffs will help your healers to keep people alive, will help your tanks to survive better and will give you up to seven "extra" DPS. Having all buffs is like raidign with 27 players instead of 20.
And now second important part - debuffs. By default bosses have 50% resistances to everything, so they are receiving only half of damage you are doing, and with having all debuffs on bosses you are lowering all their mitigation to 36%, so it is effectively +14% damage, or almost 3 extra players on top. So it is like raiding with 30 already (actually more, because that is increasing all the damage from buffs).
Next part of debuffs are about Deflects. You need to have one big 5% debuff on your raid (Telekinetic Storm, Razor Disk) and 2.5% debuff from True Strike fusion rune in gloves of at least one raid member. This is very important debuff, because it can significantly lower your raid damage output. Without those debuffs raid will have 7.5+% chance to have their attacks deflected. So it is on average 7.5% damage loss. However, some powerful or important attacks could be deflected (Esper finishers or Slinger Charged Shot for example), - it will be big spell hit loss and loss of all buffs this spell is giving for the caster. So this can cause somewhat from 5% and up to 20% damage loss.
Let's say your raid have 100k damage. Without deflect debuffs this raid will do 80~95k damage. While with all buffs and debuffs your raid will be doing near 170k damage on average. As you can see - it is insane, almost double raid DPS output! On progression it is especially important - more DPS means easier checks, more room for error. Bosses are dying faster - less time for people to make a mistake or die. Bringing one additional buff can be the difference between 3 hours of wiping and a clean kill.
List of most important raid buffs and debuffs:
First AoE Buffs:
Powerlink, PL, tier 8 (Warriors) — +8% damage, +6% Armor Pierce.
Void Pact, VP, tier 8 (Spellslinger) — increase Assault and Support Power by 12%.
Bloodthirst, BT, tier 8 for DPS, tier 3 for tank with Divine class set (Stalker) — +8% damage.
Empovering Probes, EMP, one tier 8 on healer, two tier 0 on two medics, one tier 3 if player have 3 extra Ability Points from matrix (Medic) — +5% damage, +5% healing.
Volatility Injection, VI, tier 0-8 (Engineer) — increase Multi-Hit Severity and Glance Chance by 8%.
Now debuffs on boss:
Critical Priority, it is an AMP unlock (Medic) — when an ally hits the enemy with Multi-Hit their Crit Chance is increased by 4%.
Pyrokinetic Flame, PF, tier 4 (Esper) — increase Assault and Support Power by 6%.
Smackdown, tier 0 (Warrior) — Reduce Physical Mitigation by 6%.
Bioshell, tier 0 (Engineer) — Reduce Tech Mitigation by 6%.
Haunt, tier 0 (Esper) — Reduce Magic Mitigation by 6%.
Punish, tier 4 (Stalker) — increase Physical Damage received by an enemy by 10%.
Fissure, tier 0 (Medic) — increase Tech Damage received by an enemy by 10%.
Arcane Missiles, tier 0 (Spellslinger) — increase Magic Damave received by an enemy by 10%.
Tank Debuff — Menacing Strikes tier 4 (Warrior) OR Frenzy tier 4 (Stalker) OR Particle Ejector tier 4 (Engineer) — Reduce all Mitigation by 4%.
Big Deflect Debuff — Telekinetic Storm tier 8 (Esper) OR Razor Disk tier 0 (Stalker) — reduce Deflect Chance by 5%.
Small Deflect Debuff — True Strike, it is Fusion Rune in Gloves (better to bring it as Crit class) — reduce enemy Deflect Chance by 2.5%.
Shredder, it is Fusion Rune in Gloves (better to bring it as Multi-Hit class) — reduce enemy Armor (and with it all mitigations) by 2.5%.
Chill, surged tier 8 (Spellslinger) — surged version is slowing enemies by 70%, it specific to Gloomclaw Frogs (you can do that with Medic's Restrictor tier 4 as well), slowing Swabbie (you can't kill him without it) and Navigation Core (you can go there with Esper's Restraint).
There are few more situational debuffs, like Shield Overload, Wounds, "+25% damage to espers"-parse buffs and Snares, but they are useful only in some specific fights.
Love your buffs and always bring them with your raid, treat them like your own children and they will give you twice as more as you could ever wanted.