Disclaimer: Different enemies have different breakbars. Following info only applies to standard dungeon/fractal bosses.
Since raw values are not known, I will use percentiles (total strength is 100%). The breakbar ticks every 0.24 seconds recharging 1.2% (5% per second).
Breaking the bar stuns and increases damage taken by 50% (both direct and condition) for 5 seconds and gives control immunity until the bar fully recharges (20 s). This means +12.5% party-wide damage if you instantly break it after the recharge.
Fear: -4% per tick. -16.67% per second.
Taunt: -3% per tick. -12.5% per second.
Immobilize: -2% per tick. -8.33% per second.
Slow: -2% per tick. -8.33% per second.
Chilled: -1.33% per tick. -5.54% per second.
Blind: -0.8% per tick. -3.33% per second.
Weakness: -0.8% per tick. -3.33% per second.
Crippled: -0.6% per tick. -2.5% per second.
Stun: -16.67% * duration
Daze: -16.67% * duration
Knockdown: -16.67% * duration
Daze 0.25s (Headshot): -16.67%
Knockdown 2x2s (Gale): -66.7%
Launch 750 (Banish): -38.7%
Launch 600 (Wild Blow): -55.3%
Launch 450 (Stomp): -38.7%
Launch 200 (Updraft): -55.3%
Knockback 400 (Gust): -25%
Knockback 240 (Kick): -25%
Pull (Scorpion Wire, Into the Void): -25%
Stone (Basilisk Venom): -25%
Ice (Deep Freeze): -50%
Ward (Ring of Warding) -25% per pass
Sigil of Paralyzation works (increased stun duration)
Pull distance doesn't matter
Enemy actions (attacking / movement) don't matter
Other enemies (compared to fractal bosses):
Mordrem Guard Punisher: Bar 16.7%. Regen 0% per tick.