Here is an early example of live action use for animation at Disney. All human characters in Snow White and the Seven Dwarfs relied on rotoscoping, except for the dwarfs. The more realistic a character concept, the more live action footage was used to help the animators get a nuanced performance on to the screen.
But rotoscoping is a tricky business. If not altered and interpreted by an animator, the result can be stiff and lifeless. Changes have to be made in order to portray these filmed performances for for graphic motion. A good animator will mess with the timing and proportions of the photostats.
Some of my favorite Disney characters who were successfully based on live action are Cruella de Vil and Roger and Anita Radcliff. Their design has various degrees of caricature, but the motion always feels reel.
Then there is Cinderella's Stepmother, a very realistic looking character based on live action, and she comes across as being very powerful.
Milt Kahl's comments about the use of live action cracks me up: "If you are going to have realistic animated human characters, I think the use of live action is necessary. If everybody on the picture was a Milt Kahl it wouldn't be necessary. But unfortunately they aren't."
Here is the Hunter from Snow White.
