Investors often require anti-dilution provisions, which protect investors from too much dilution in subsequent rounds of financing. That way, if the company sells shares in a future round at a lower price than it is selling them for now, in this round-the down round. Preferred shares offer some favors, for example, an elevated position in the liquidation events or at the distribution of dividends. Such privileges do not exist on common shares, which are typically held by founders. Negotiation between preferred and common shares boils down to where, how much protection, and return compared to founders and other stakeholders investor will be entitled to.