I can't speak for other Dommes, but to say I have "broken" someone or want to "break" someone is used a bit tongue and cheek. Pushing someone's limits or having a breakthrough moment in training is not breaking a sub - at least not to Me.

In the few instances where a sub really breaks down in session, a ton of aftercare is needed to bring him/her back to a solid, stable, healthy place. I have experienced this more in lifestyle scenes than in pro sessions.