A special class of hybrid systems, that occurs in many applications, are the piecewise affine systems. Due to their nonlinearity, they may often be difficult to analyse. Therefore, different approximating methods have been developed for analysis, verification and control design. This paper considers one such method, and gives some methods for investigating how sensitive it is to changes in the dynamics and switching points of the real system. This method can be used either for robustness analysis or for control design.