Roth 401(k)s and 403(b)s

I am interested in: 1. Why should retirement plan advisers offer Roth 401(k)s or Roth 403(b)s to participants? 2. What should plan sponsors know about Roth accounts? 3. What should plan sponsors teach participants about Roth accounts and what participants are likely to benefit the most from them? 4. Also, how do in-plan conversions from pre-tax to Roth work?