We illustrate some fundamental alterations of the solar wind - magnetosphere interaction that occur during low Mach number solar wind. We show that low Mach number solar wind conditions are often characteristic of coronal mass ejections (CME), and magnetic clouds in particular. The implications of this unusual mode of interaction, for which the magnetosheath plays a pivotal role, have generally been overlooked. These may include: (1) asymmetric magnetosheath flows; (2) asymmetric magnetopause shapes; (3) changes in the development of the Kelvin-Helmholtz instability and giant spiral auroral features; (4) variations in the factors controlling dayside magnetic reconnection; (5) cross polar cap potential saturation; and (6) sawtooth oscillations. We highlight these expectations primarily by use of global MHD simulations. We discuss the mechanisms that rule such an altered interaction and how the implications may be important during CME-driven storms at Earth, as well as at other astronomical bodies such as Mercury.