Why do animated characters look like their voice actors?

[I_M_Melancholy]

Is this a common practice? Or is it more to let people get a feel for who is voicing who in animated movies?

Examples would be Whoopi Goldberg as Shenzi in The Lion King
All the main characters form the Emperor's New Groove etc.

 

[jakezinho]

finding nemo, toy story, shrek (kinda), well i guess its a disney thing and yes i knwo shrek isnt disney