It's all about natural drawing/painting.
When you use traditional art tools every aspect of your stroke is felt. The angle you hold a pencil/brush, the way to turn the pencil/brush as you draw, how hard you press, etc. The goal of tablets with additional dynamics is to more closely mimic natural drawing. It's not about using "tilt for shading" it's about seeing every aspect of your drawing.
The more dynamics a tablet reads, the more natural your drawing/painting will feel (if dynamics are configured correctly).
You can generally do without tilt and rotation unless you are creating full, detailed illustrations. For general use tilt and rotation won't have a great deal of use. However, both tilt and rotation can be very handy if you are accustomed to varying your stroke as you draw/paint with a pencil/brush. Many artist have a technique of "rolling" the drawing device around within their fingers creating different angles which meet the drawing/painting surface. It's this use that is most noted when you've got the ability to see tilt and rotation in a stylus.