For most Disney animated feature productions the research that helps to get the best results on the screen seems endless. Before animation begins storyboards are drawn and redrawn, various styles are being explored in order to achieve the right look for the film, and often live action is shot to help animators with their acting choices.
For the movie Peter Pan a lot of live action footage was filmed, and the super talented animators knew just how to use it. If the acting was inspired, why not incorporate it into your animation?
Usually timing and staging needed to be altered, because graphic animation has its own rules. Broader action, more squash and stretch and a clear silhouette.
I just love looking at these vintage photostats that were made available to the animators.
You can see what motivated them and how they translated the footage into graphic motion. Sometimes they would ignore the live action and create a different performance on their own. But as Marc Davis said, it was often helpful to be able to look at something instead of starting with a blank sheet of paper.
I myself worked with live action reference for Gaston and Hercules. We did it the same way by filming the actors wearing somewhat crude outfits, and by using the simplest of props to create some kind of an environment for the scene.
Sometimes those on the set were laughing so hard at how ridiculous (yet useful) the footage came out. If the studio could only make that footage available to you guys, you would laugh you head off.
Artists like Mary Blair preferred to present sceneries, characters and colors in an almost abstract way. With a strong focus on lighting, emotional color choices and simple staging these studies were the inspiration for the final artwork. Sure, the production backgrounds have a more realistic stage set feel, but Mary's influence is very apparent.
Eywind Earle took a similar approach for Sleeping Beauty and so did Walt Peregoy for 101 Dalmatians.
In the end this and other films landed somewhere in-between realistic and abstract influences.
And I do believe that's one reason for their greatness.