It's pretty crazy how expensive a simple sprint planning meeting really is if you have 5+ engineers.
Sometimes it leads the death of many man-month projects, or worse.
An assertive dev will look at the requirements, try to figure out how that fits, and then reply back to stakeholders if it's unfeasible. Everyone else will sit there for a week bashing their brains out against a keyboard and have continually increased anxiety because they've been assigned an impossible task. The time for a dev to be involved in the process is during requirements gathering as a partner to the process, not after a contract for work has been signed by the client.