A common question asked by investors is "What are your CACs?". The real question is "What will your CACs be if you invest 10-20M in sales & marketing?" Finding scalable and profitable customer acquisition channels is crucial for Series B and after. There are many challenges ahead, but if this is figured out at 5-10M ARR, it's an excellent (and rare) spot. Consumer startups can sometimes rely on expanding their existing acquisition channel (e.g. TV, YouTube, Facebook, etc.) because they have an enormous audience. In B2B this is very rare because there is too much ad wastage and targeted ads won't have volume to absorb 10x spend.

The underlying problem is that the existing "hot demand" for your product - people who are actively looking for it - is usually quite limited. The good news is that the "lukewarm demand" - companies that would benefit but aren't aware of it - can be much larger. This is why content marketing is so critical in SaaS: it allows you to capture leads at an earlier stage of the discovery process. However, scaling up content marketing by 10x is not as simple as 10x spend.

How do you know in B2B SaaS, if you've found scalable acquisition channels? One great sign is that if you can hire salespeople and they meet their quota. Equally important, it shows that the sales process has matured beyond founder-led sales - it doesn't take founders or superstars to sell, just "normal" people. In addition, it shows that you've managed to attract the right people; set up the right processes and infrastructure; create the right incentive structure; and culture for a successful sales team.

1. Are you able to make outbound sales work? Doing outbound at reasonable CACs is usually very hard because you deal with lots of unqualified leads; AEs and sales leaders need a bunch of persistence; and founders need strong commitment because a serious attempt to succeed at outbound sales costs major money and time. If it works, it can be a highly scalable customer acquisition channel
2. Have you managed to increase your search engine marketing (SEM) budget consistently and significantly without negative effect on CACs? What is your impression share, and how large is the search volume that you can still tap into? As mentioned, past performance in scaling an SEM budget from A to B alone is not a reliable indicator of future performance but can be impactful when combined with thorough analysis of relevant search volume.
3. Have you built a content marketing "machine" that consistently generates more leads month-over-month? If you can consistently increase inbound/content leads for some time, it means that you've found your narrative, or "North Star"; started to build content distribution channels; and managed to attract the right marketing people and have them be effective.

Source: http://christophjanz.blogspot.com/2017/10/knowing-when-to-scale-and-how-to-prove.html