Advantages: To know the advantages that the Spellbreaker class provides you must first understand how debuff stacking works. In short, it doesn't. If you have two debuffs directly applying a reduction to attack speed, only the strongest one will apply to the enemy. The Spellbreaker class is rather unique in the fact that none of the debuffs applied through the Warfare or Spirit skill trees overlap, allowing you to apply more and more debilitating effects your enemies.
A list of the debuffs available to the Spellbreaker:
Deathchill Aura / Ravages of Time / Necrosis
% Reduction to Enemy HP
-% Total Speed
% Reduction to Total Damage
% Reduction to Armor Absorption
Absolute Reductions to Bleeding, Vitality, and Life Leech Resistances.
% Physical Damage Reduction
Absolute Reduction to Physical Resistance
Absolute Reduction to Stun Resistance
% Defensive Ability Reduction
Reduction to enemy Armor
% Movement Speed Reduction
All of these effects apply with no overlap. Deathchill Aura reduces total speed, and Hamstring only reduces movement speed, since both are not trying to reduce the same value directly both apply. Similarly Ravages of Time Reduces Total Damage and Triumph only affects Physical Damage. Ravages of Time affects Armor Absorption while Hamstring affects the armor value itself.
In truth, everything just works together so well. Some notable examples would be the Necrosis upgrade for Deathchill Aura; Since '% Reduction to Enemy HP' is based on Vitality Resistance, the Ravages of Time skill will deal noticeably more damage. Necrosis will also assist your Liche King's damage output as all his skills deal Elemental, Vitality and '% Reduction to Enemy HP'. However, since '% Reduction to Enemy HP' is always based on current HP, not Max HP, Ravages of Time, and Necrosis should not be relied upon as a damage dealing skill and instead be used as a utility based one.
Necrosis will similarly benefit War Horn (Doom Horn), and Slam abilities due to the Vitality Resistance Reduction.
Necrosis will benefit your Dual Wield skills that apply bleed, and the Lacerate (War Wind) skill due to the Bleeding Resistance Reduction
Disadvantages: The Spellbreaker class is largely a rather boring class to play due to it's heavy reliance on passive abilities. The few active abilities you do have tend to have niche uses, long cooldowns, and high mana costs. The Spellbreaker is highly specialized in Melee combat an as such will have some difficulty dealing with ranged enemies, notably, enemy archers. Keeping your Piercing Resistance as high as possible at all times will however offset most of the the danger they pose. Every ability the Spellbreaker has access to has a use that benefits the class, but there is always a trade off; be it in the number of skill points required for the skill tree to shine, the high mana costs, or even the cooldowns associated with the ability, your always going to have a problem to fix with your gear.
Boss Killing Abilities (Battle Standard, Ancestral Horn, Summon Outsider) Subject to Long Cooldowns and High Mana Cost
Utility Based (Doom Horn, Vision of Death, Circle of Power, Soul Vortex) Subject to specific circumstances
Requires Unique Gear & Playstyle to make full use of. (Dark Covenant)
Leaving you with only four skills in which to use regularly. (War Horn, War Wind, Slam, Vision of Death)
Furthermore, unlike similar classes like the Conquerer or the Warden, the Spellbreaker is a slow class to play, only really coming into it's potential past level 40 when you're finally able to reap the benefits of the Dual Wield skill tree, as before level 40 your going to be hard pressed into Distributing your skill points into the other passive abilities to keep yourself alive.
Warfare Mastery Skills