Having quality leather bring sturdiness and flexibility, the warmth produced by the body adds suppleness to the construction, allowing it to re-mold itself into a closer shape; a feature, no matter how interesting, one that also needs to be contained in order to prevent that repetitive movements could overstretch the leather.
Ironing the interfacing was a great way to afix it onto the leather before securing the pieces with stitchings to keep them there.