The benefits, as with every Buddha's practice, is two fold - the benefit you gain for yourself, and the benefit that you can bring to others.
So as a summary of what has been said, the benefits to us on an individual level, is that his practice helps us to tame our crazy up-and-down minds, calm us down to gain more control over our minds, emotions, reactions etc. As the speech emanation and of course, as an emanation of Manjushri, Wangtse's practice also helps us to gain mastery over our speech, that we can have great positive effect on others by our speech and speak in a way that is pleasant and attractive. Surely, all of us would love to have people listen to us when we speak!
On an inter-personal level, the practice of Wangtse helps us to develop the skilful means and wisdom to be able to control and tame others' difficult minds. This is done mainly through the medium of communication - speech, writing etc. We speak in ways that will affect their minds positively to calm them down. Calming someone down doesn't necessarily mean that they are angersome, violent, aggressive etc. it means that their minds are very unfocused, distracted, easily overrun and controlled by their emotions, jumpy, inconsistent etc. When we "calm them down", it is to "calm" their minds from the aggressive distractions of samsara, and turn their minds to the more truthful peace of Dharma. When their minds are calmer, and more still, they can open up to teachings, absorb the knowledge, understand and therefore begin to practice and apply it to their lives to bring transformation for themselves.
