The problem
Hall-effect and other magnetic sensors read the field of a target magnet. With a conventional or simple multipole magnet, the field shape is fixed by the part you can buy, and the mechanical feel of the control, such as detents in a dial, needs separate parts.
How coded magnets help
Correlated Magnetics Research's About page shows a magnet patterned for a Hall-effect sensor application among its examples. At CES 2015 CMR and AKM Semiconductor demonstrated customizable magnetic sensing controls. In the example described in CMR's press release, a wireless dimmer used one round magnet with concentric patterns: an outer ring read by AKM's rotational Hall-effect sensor to detect position, and inner rings that gave a tuned detent feel at set rotational positions.
That combination, sensing and haptic feel from one patterned part, is the case for coded magnets in controls. It can reduce part count in knobs, dials and selectors and keeps the mechanism contact-free.