The role of billing in the life of a SAAS start-up is absolutely key, even if well funded. So also is the investment in the product. The toughest scenario is that you invest in the product upfront, and then have a pay at the end of the term structure.

Much, much better, bill upfront and then build the extra features - which is possible in Enterprise sales because the whole sales & implementation process is often so slow. If you can do that, even if not for the whole amount, your cash flow is much stronger and your risks massively lower.

So 'if you build it, they will come' might instead be 'bill it, then run as fast as you can to build it'!

I encourage you to read the post by Tomasz Tunguz below - he maybe analytical but also talks a lot of common sense.