In the Planning tutorial, I asked you to read a paper suggesting that we need planners to understand other people's plans as well as to create our own. That was chapter 26 of Thinking --- Readings in Cognitive Science, edited by P.N.Johnson-Laird and P.C.Wason. There was a more recent account in Chapter 10 of Artificial Intelligence by Charniak and McDermott, concerning attribution of emotions to the characters.
Perhaps an understander needs emotions too. The article on Emotional modelling in the Encyclopaedia of AI gives a brief account of this. Beyond the Schema Given in Cognition and Emotion number 1 volume 3 is the most accessible reference.