The Importance of Speaking in Formal or Informal Style

Adnan on Facebook asked me this during the IELTS exam in speaking, do we have to speak in a formal or informal way? Right. The language you want to use is the same that you would use if you were going for a career job interview. But it's not the kind of slang English that you hear with your friends in the pub. It's sort of a professional style. You don't want it so stiff and rigid that you sound pompous. In English, our neutral style is fairly informal to an extent.