This warcry boosts damage substantially. The amount of Fury required sounds considerable, but in the BlizzCon demo a Barbarian of around lvl 6 or 7 had about 100 Fury, and could fill the bulb in a battle with just 4 or 5 enemies. The duration at level 1 wasn't long enough to last between battles, so players had to remember to cast this one as soon as they had enough Fury, just after a battle started. Remembering to recast it during longer battles was trickier. Presumably  The Perseverence skill increases the duration of this and other warcries, so more points will add to in this one would presumably increase the duration, but that's not yet knowndamage bonuses.