For a startup, capital commitments over time (even on a monthly basis) are always better than a lump sum in the beginning. If the VC money is used to build things, the startup can't spend the money as quickly as investors want. The extra cash distracts founders to build side projects, prepare plan Bs or Cs or scale too fast. A good rolling fund allows investors to defer cash transfers, slightly cheapening the deal, but also continuously monitor the use of cash over time. For the startup, it gives them the most important asset they can't buy: time.