People often confuse startup speed with agility. The talk "Agility ≠ Speed" does a good job of critiquing that idea. Agility is about the ability to change direction gracefully. NoSQL definitely gets you started quickly—as OP noted, you avoid much of the overhead of data modeling and making changes to schemas—but at a certain point you can get into real trouble, and that will slam the brakes on your velocity. I've experienced the same thing with weakly typed languages. These sorts of tools can be very useful in the right use cases, but trading away some of the guardrails can extract a large cost if you aren't thoughtful and careful.