Optimizing how much energy is recapturedThe upcoming Cadillac ELR, a sportier and more luxurious descendent of the Chevrolet Volt, will feature steering-mounted paddles, but they won't be used for shifting (electric cars generally don't need multi-speed transmission because of the flat torque curve characteristic of electric motors). Instead, pulling a paddle will trigger regenerative braking. This regen-on-demand will be more aggressive than the regen that takes place when just coasting, but it also won't bring the ELR to a full stop or engage friction braking, unlike the brake pedal, which blends regen and friction.
The idea is both to help drivers recapture more kinetic energy and store it back in the batteries and make driving this plug-in hybrid more fun:
“Regen on Demand enables ELR drivers to actively re-capture energy when slowing down, such as when approaching slower traffic or setting up for a tight turn,” said Chris Thomason, ELR chief engineer. “This allows the driver to take more active role in the electric vehicle driving experience.”[...] Releasing the paddle disengages Regen on Demand, allowing the vehicle to coast normally. The driver can engage and disengage Regen on Demand as desired and as traffic conditions allow.
“Pulling back on the paddle to slow down allows the ELR driver to keep their foot close to the throttle, ready to accelerate,” Thomason said. “It provides a more engaged, satisfying driving experience, and when you consider the added benefit of re-capturing energy, it’s also a smart thing to do.” (source)