Render farms for animation use programs to organize what computer is rendering what frame of a scene. There would be one computer that kinda keeps track of the progress of the others, such that when one computer goes "im done with frame xyz", that computer then tells it to start on frame yzx. As each frame of the animation might take different amounts of time, so one computer might crank through 5 frames in the time it takes another computer to do 1 frame.
also a render farm is using MANY computers to render at one time. If you have a 1000 frame scene, and 100 computers doing the calculations, instead of taking your computer the 1000 frames worth of rendering, it would (theoretically) take those 100 computers to do it in 1/100th of the time, as each computer would crank out 10 images before being done, instead of yourself doing 1000 frames.
