2D Animation has traditionally been very expensive because every frame must be drawn by hand. Even with todays digital inking and painting software, the process still relies on individuals hand-drawing each frame. This laborious task is called "tweening".
Synfig eliminates the task of manual tweening, producing smooth, fluid motion without the animator having to draw out each frame individually. This allows you to produce 2D animation with fewer people while producing art of a higher quality.