One of our goals as pronunciation "clinicians" is always to help learners become more confident in speaking the language. Just better intelligibility should result in appreciable gains from that perspective. Of course, there is more to effective face-to-face communication than just the quality and accuracy of speech. To be persuasive, one must be perceived as credible as well. Some part of that is nonverbal. The research and "friendly advice" (such as that linked above--caveat emptor!) on that focusing on business and romance is all over the map, especially when cross-cultural norms are factored in. For example, ability to detect lies (as opposed to simple discomfort or disgust) by the untrained is generally no better than random--despite what the TV program "Lie to Me!" projected--before it was cancelled! But picking up the signals of confidence, or lack of it, in the speaker is another matter. Good posture, rhythmic body movement synchronized with speech, appropriate use of gesture and eye contact--in addition to intelligible pronunciation-- all contribute to the credibility of the message. Pronunciation work is a perfect venue for helping students add to their repertoire of handy identities, including an acceptable "business-like" persona to have available for engagements where one is in order. To do that, requires systematic practice in the optimal body movement and gesture management styles of that culture--even if you, personally, don't have a business suit. In other words, make sure you at least occasionally "stick to business."