I would imagine having good answers to people's questions is a byproduct of thinking through the approach you're taking with your product / company. And writing it would have value beyond just replying to people's issues, it could be useful institutional knowledge for future employees to help them more deeply understand the product / company. Being explicit with your reasoning also empowers employees to determine where the reasoning may break down as time and context change (vs thinking the leadership has it all figured out).
I can see that value, although as a new venture, I'd still be somewhat skeptical that this would be the very most important thing the team could be doing. Institutional memory doesn't provide a whole lot of value until you have an operational business.
Although, to undercut that point, if you're prepping for pitches, I can see the value, for sure.
But what I'm still not seeing is why bother trying to anticipate beforehand.
