the reason for tracing paper

I've been doing a tiny series of works where I overlay a selected number of photos of Western Heights with tracing paper and drawing over it (I'll upload a picture of them a little later, but for now, here's an example I found on the internet).

This is inspired by a process in traditional animation where people draw frame-by-frame animation by using tracing paper. 

While I'm really interested in getting into the animation business, I've never used this sort of paper in my whole life, so by giving this a go, it's definitely a new experience for me.