I thought I covered that above; the 32+ tons is carried to provide a reserve to cover the case of one or more engine failures during ascent and to still achieve orbit. To carry less would turn a mission survival failure into a mission failure.
In the event all or part isn't used, the first stage can still be recovered; turning a necessity into a virtue.
Last edited by ORAC; 19th January 2016 at 16:06.