I don't just use reference for animating movement, I also reference for most of my backgrounds as I can never think of how to plan out rooms for example so reference helps with understand how big a door should be in comparison to a character for example.
Now for almost referencing I prefer to use live action and real life, so nothing that has been created by humans or drawn, just because I feel like if I was referencing a hand and I just referenced a drawing of a hand it would basically be like copying and I wouldn't develop my own techniques in any way. That being said, in my animation there is a scene where the studying sister squeezes the annoying sister's head and it explodes, and there isn't a great deal of live-action reference material for that. So I had to look at how they do it in animation and the most useful reference material I found was in the animated series South Park.
The head explosion scene took four days to animate even though it was only around six frames long so half a second. The reasons for this justified the amount of time taken as not only was it highly complicated to figure out but I also had to incorporate colour which added to how complicated the scene was to animate.
In the end I feel it looked very successful although I wish I didn't have to reference South Park so much for it as that does feel like slightly cheating, although if it wasn't for the clip I referenced I would have had no idea about how to go about animating the scene.