The same as the importances of regular animation... except better technology to enhance enjoyment. =]
As humans, most of us are attracted to bright objects (believe it or not) and technology is helping us get addicted to them.
Computers also make animating much easier for the creators. Think of it this way- the old Disney films like Sleeping Beauty were drawn by hand. The creators had many sheets of papers with drawings, sketches, and paintings of the backgrounds. It was harder to keep track of.
With the computer, however, companies such as Cartoon Network can use specific programs to create animation easily without using tons of paper.. all they need is one computer screen, skilled artists, the capability to copy images on the computer with a click of a mouse, other details such as music and voice actors... and voila! An updated and polished looking animation is created!
The easiest way to animate is to use Flash or ImageReady and Photoshop.
There are those who want to make cartoon characters more realistic though- without making them into humans. That's when 3D animation kicks in. With a lot of hard work and special effects, people can make stuff like Toy Story 1 and 2, Shrek 1 and 2, A Bug's Life...and so on.
Basically, the computer stuff adds to the quality of the animation and the technology enhances things to new levels- it'll get even better in the future. Who knows? Maybe some day they'll make animation that turn even more realistic by using holographic effects- the cartoon characters may end up in ur living room or wherever ur watching the show... instead of in the TV.