As of this writing (February 21. 2005), this is arguably the worst ability the warrior has. The damage is paltry, the rage is expensive, and the debuff is too short and too weak to be of much use. Its use is so limited that any specific situation it could be used in would be so anomalous it wouldn't be worth taking a slot up in your toolbar. Get this ability only to experiment with until you're convinced, then never touch it again.
This is also one of the few abilties where upgrading its rank is not worth the price. The only aspect the increases is the damage, which is negligible to begin with. Cleave is a much better ability to use when fighting multiple enemies.
Edit: This ability is useful, just very little, when attacking mobs that have high attack speeds or more than one mob, use this to save some HP if you don't need the extra rage.
Edit, Jan 06: I have to disagree with the above. Damage is pathetic, but your taking away 10% of an enemies DPS for up to 30 seconds. Throw a Demoralizing shout on there, and you are significantly reducing the damage you are taking.
Edit, Feb 06: Thunder Clap is at its most useful at low level (up to 14-15). I personally have used TC extensively to fight my way out from under a three-way aggrofest. It also generates pretty good agg, making it useful for drawing enemies away from the clothies.
Edit: Feb 06, use to draw intial aggro with mobs so that they hit you, build up your rage, and allow more mob control. I still use(sparringly, and when needed) TC at lvl 60 while OT so that i can maintain mobs that are around me by constantly knocking myself up on there agg charts.
Edit:Aug 15: Remember, this is the ONLY multi hit skill avalible to Warriors under lvl 20. My warrior has used it whenever there are 3+ enemys around... and will continue to until he hits lvl 20 and gets cleave.
Edit: Does Thunderclap work against totems? Seems Thunderclap could be useful in PvP against a Shaman. Wait until the Shaman has dropped two or three totems, then thunderclap to destroy them all? Totems only have 5hp.'
Thunder Clap doesn't destroy totems--they're unaffected by any skill that doesn't specifically target them (all AoEs, as well as chain target attacks such as Cleave UNLESS the first target is a totem). Other than that... Charge + TC is a good opener when you can safely charge in an instance, since it'll cut down on the damage you're taking and get some initial aggro going. Also useful if you're trying to solo an elite or something, since taking even one less hit in those situations is often a hefty chunk of your health bar. My0p1c 18:53, 2 September 2006 (EDT)
Regarding max threat available from tclap, doesn't the 1.15 multiplier from 3 points in the Defiance talent also apply to this ability? so 123*200%*90%*175%*130%*115%=597
Oct 16: TC has become usable in Defensive stance in recent patches and has become much more useful. I find it effective while tanking 2-4 mobs and am able to stay above healing aggro on all of them quite easily, then I just need to Slam and Revenge or Sunder on the current target being killed to stay above dps on threat. Not to mention it can remove a fair chunk of the incomming damage, especially when talented. - Mutilor