New results from the global MHD simulation GUMICS-4 show that the energy transfer rate from the solar wind into the magnetosphere is a function of also the past values of the IMF. Furthermore, comparison of the energy input rate with the conversion and dissipation rates in the magnetosphere and ionosphere shows that the energy entering the magnetosphere is processed by the system without delay. This and earlier observations lead us to suggest that the role of energy input during the substorm growth phase is to facilitate the configuration change rather than to store energy for later dissipation. While the change of magnetotail stability requires configuration change, the substorm energetics after the onset is quite directly driven by the solar wind energy input.