They have no impact on our understanding of the present universe, only perhaps on the details of what happened AT the Big Bang itself. If true, superstring theory predicts that our 4-dimensional space-time dissolved into some other very bizarre 'object' in which space and time as we know these concepts can not be used to describe the conditions prevailing then. We do not know if superstring theory is correct or not because it has yet to make a single testable prediction.