Many movies these days are created using animation. Films like Shrek and Finding Nemo gained a massive profit from people watching the film and buying the merchandise.
Two of the greatest advantages of using computer animation on a project is the realism and speed computer animation can bring to a project. For example, once an image is created in the animation program, it can be stored there for later use; it doesn't have to be "redrawn" or recreated. For shows produced weekly, this saves a great deal of time. While the initial output to create the product is steep, the later episodes of a production go faster, because the key images have already been created.
In terms of realism, one need only think of the battle sequences in the "Lord of the Rings" films. Created on a program called Massive  Not only did this program offer speed to the project, creating thousands upon thousands of warriors for huge battle sequences, it was able to do so faster than anyone could hand draw that many individual characters. Additionally, the program provided realism to the sequence. Each soldier, whether Ork or Elf, was a realistic, single character. This program coupled with sequences of shots of live actors in costume provided believable and realistic results. 
Any computer animation is limited often by the program's limitations. In order to understand this, one need only to think of the various versions of different video games. The earliest incarnations of a game like "Tomb Raider" look different than the later, more realistic versions of the game does. These changes are due in large part to the advances in technology, which have a direct effect on what the computer animation program can do. If the technology is limited, the program is limited. 
An animator must also take into consideration what each stage of the task calls for. A pencil drawn image often leads to a spontaneous image, full of feelings and emotions that are often difficult to convey with a computer animation program. Such graphics are vital to the early stages of a project when it's being fleshed out. The rendering of characters lends itself to using pencil drawn or hand painted images for this reason. Because there is no pressure to produce a finished product, the artistic team is free to explore, to doodle, in order to get a character just right.

The phi phenomenon is the optical illusion of perceiving a series of still images, when viewed in rapid succession, as continuous motion. Max Wertheimer, one of the three founders of Gestalt psychology, defined this phenomenon in 1912.

 

 

Beta movement:  

Beta movement is an optical illusion, first described by Max Wertheimer in 1912, whereby a series of static images on a screen creates the illusion of a smoothly flowing scene. This occurs when the frame rate is greater than 10 to 12 separate images per second. 

 

The phi phenomenon is similar to beta movement in that both cause sensation of movement. However, the phi phenomenon is an apparent movement caused by luminous impulses in sequence, whereas beta movement is an apparent movement caused by luminous stationary impulses

^{PERSISTENCE OF VISION}
 whereby multiple discrete images blend into a single image in the human mind and believed to be the explanation for motion perception in cinema and animated films.

BETA MOVEMENT 
 s an optical illusion, first described by Max Wertheimer in 1912, whereby a series of static images on a screen creates the illusion of a smoothly flowing scene. This occurs when the frame rate is greater than 10 to 12 separate images per second.