Whether or not a startup and an investor take the secondary letter with a safe is now a decision that the parties will make, and it can depend on a large number of factors. Among the factors to be taken into account, there may be (among others) the purchase amount of the safe and the amount of future dilution that the proportional fee will entail for the founders – an amount that can now be predicted with much more precision if post-money safes are used. For a growing startup, the company is likely to raise more money. As a start-up investor, I`m not interested in paying it back. .