Retention rate is really important, because it has a huge impact on how many subscription payments you can collect over the lifetime cycle of a customer account. It will help you to increase your customer LTV by a lot.
The retention rate, the revenue per user and the lifetime value of a user are also really important if you want to get into a program such as YCombinator. Spending money on marketing is not as important as having really good unit economics on a per-user basis.
