[Bicycle Bob]

Any braking wastes momentum; typically, people coast a bit to use the momentum and make the braking "easy."
Hard cornering also wastes energy, but not as much as braking to a lower cornering speed. Tires with a side slip angle are like tires running up a slope of that angle, bearing the side force as weight. This action will do the work of brakes to use up any surplus momentum, but trying to maintain speed or accelerating through the corner defeats that automatic fine-tuning.
If you don't have time or inclination to coast down to a moderate cornering speed, the most economical option is to scrub off some speed in the corner and then accelerate on the straight. Unfortunately, this is not as safe a way to get sideways as going in slow and accelerating in the corner.

Engine braking is usually used on manual transmissions, but yes, you are finding it. On diesel trucks, the engine braking is sometimes enhanced by a noisy, spring-loaded exhaust restriction, or Jake Brake, which is what those signs are about.