Some designers like to work on a product piece by piece.
They focus on one screen or feature at a time, and dedicate full days of work trying to make that one piece look as polished and finished as possible. Before sharing it with the rest of the team, they make sure visuals are pixel perfect, elements are precisely aligned, imagery and copy are as close to final as possible, and that they actually prototype how the elements in screen will animate together.
And they never share their designs with the rest of the team until they feel extremely confident about the work.
But there are a few inherent risks with that approach.