I do actually agree that some amount of planning, and especially putting down a sketch on paper do help, in particular as a way to nail down requirements and figuring out obvious roadstops, but it is important to be under no illusion that the final project will resemble in any way the plan

> But assuming everything will change and using that as an excuse not to plan at all sounds like a poor choice to me.

I know that's how it sounds. But in my experience it turns out to be a lot more effective than planning.