I think you are conflating two separate, but related issues: 1) Raising large sums of money, when is it right? 2) Having a business model. For the business mod

I think you are conflating two separate, but related issues: 1) Raising large sums of money, when is it right? 2) Having a business model. For the business model, yes, you should have one and you should put considerable thought into it. You should always test it's validity given the market at that moment in time or in the foreseeable future. That said, if you are Twitter, you are affecting fundamental changes in communication and your impact is evident on the societal level. At that level of impact, you have the luxury and duty to take time to really work out the kinks from your business model. Now, if you are not Twitter, raising money during a bubble or looser years and using it wisely could be the difference between life or death (or layoffs) during not so good years. Having money in the bank is powerful, whether you are putting it there or your investors are. Just be careful not to have such a high burn rate that you cannot hope to cover it with your own revenues should push come to shove.