In the comments section of Does it matter if I use \textit or \it, \bfseries or \bf, etc, I asked for a clarification of these points. The clarification has mostly been made, but it was requested that I turn this into a question to provide for more room for this question to be fielded.
So here it is:
Please explain the difference between \emph
and \textit
. When should they be used, respectively?