Tell Claude Code to "build the user feature" and it works through it one piece at a time. Types, then the model, then the routes, then tests, then docs. One agent, one long line of work. It gets there, but you wait for the whole chain even when half of it could have run at once.
Now tell it to "use five agents and go fast." Sometimes that works. Often two agents write their own version of the same type, a third edits a file a fourth is also editing, and you burn the time you saved cleaning up the collision. Naive parallel work trades a slow run for a messy one.
