A board member insists on a feature that you believe adds no value. How do you handle it?

I treat it as a value question rather than a technical one, and I try to do that before the relationship gets adversarial.

1. First I ask what outcome they are protecting. Very often the stated feature is a proxy for a real concern — “I want a field for X” usually means “I do not trust that we will follow up on X”.
2. Then I map it against the vision and value map. If it supports a stated outcome, it belongs in the backlog and the conversation is about priority. If it does not, the map is the neutral ground on which to say so.
3. If it is genuinely low value but cheap and politically important, I will often build it and say plainly that it is being built for that reason. Consultants lose credibility by fighting every small battle.
4. What I will not do is quietly absorb it into scope. Unowned scope is how small projects become late ones, and a board member who was told the cost can make an informed choice.