So many times I find myself trying to extend emotional moments that interviewees give to us because very often its only for a few seconds.  Those fleeting moments can make a message so powerful if edited properly.  As I edit documentaries and other story driven projects, I'm always compressing or decompressing moments in order to elongate or speedup the pace.  This pacing is what gives viewers emotional reactions to our story telling.  It can be for kinetic (energized) reasons or for emotion and drama.  This editor has such a great explanation of the science behind this concept.