The most empirically-supported treatment for the various anxiety disorders (panic, phobias, OCD, PTSD), is called "exposure and response prevention" - in other words, a guided process of exposure to triggers for anxiety while preventing "safety behaviors" (ways of stopping/avoiding the anxiety without dealing with the trigger). The person experiences anxiety in response to the trigger, but waits for the anxiety to dissipate (like other emotions, when allowed to happen, anxiety peaks and then lessens on its own). Each time the person is exposed to the trigger the "peak" of anxiety is less intense, as a result of the previous exposures, until eventually the trigger is no longer triggering.
DBT expands the use of exposure, to apply to any emotion that causes a client problems in functioning (e.g., anger, guilt, shame, fear). It also expands our understanding of exposure to include anything that evokes the immediate or remembered experience of the emotion. Finally, it clarifies that the exposure has to include a "corrective" experience - in other words, the exposure should not reinforce the problematic emotional response, but should "correct" in with incongruent information or an incompatible emotional response. The same principle applies with classic exposure and response prevention - the idea is that when nothing bad happens as a result of exposure to a feared trigger, the fear begins to be disproven.
Based on all of this, it seems obvious that, for therapy to be effective, it is necessary for it to expose clients to the distressing emotions (and triggers thereof) that are causing problems for them. However, while doing so, it's also important to keep the overall level of emotional arousal within the "therapeutic window" - neither so little arousal that there is no real exposure to the emotions, nor so much arousal that the client's internal processing system is overwhelmed and the exposure itself becomes traumatic.
In group therapy, a significant challenge is to keep exposure to emotions within each individual group member's therapeutic window, so that nobody is traumatized, but everyone has the opportunity for growth. I've been filling in at a day program location (while waiting for my own location to open) that has dealt with concern about group process becoming traumatizing for someone by making it their policy to avoid triggering anyone (i.e., to avoid exposure altogether). As a result, everyone tip-toes around the issues, and nobody work through the issues that brought them to the program. Yesterday, one of my clients expressed frustration with this dynamic, and i have to say I'm frustrated too.
So, what is the answer? How do we bring emotional exposure into the therapeutic window, when clients are at very different levels of emotional tolerance/arousal? I'm interested in hearing your suggestions!