According to the manual, the B gear should be used on slopes to slow down the car without stressing the brakes.
Some people say that B gives a better grip on snowy roads, even on flat ones.
Since we had snow a couple of days ago, I've done some tests.
No hills here, so just flat, icy roads.
The B allows you to slow down approaching crossroads without touching the brakes: it may somewhat confuse the drivers that follow.
Anyway, while driving with the B on, and cruising at constant speed, I noticed an higher noise level than usual: the engine was running at high RPM rate.
At 68 km/h instant mileage was 6.2 l/100km
Shifting back to the D gear lowered consumption back to 5.0 - 5.2 l/100km.
I asked some Prius and Auris drivers, and it seems in those cars, driving in B, on a plain road, is just the same as driving in D, with no different RPM rates.
Is this a different behavior of the Yaris Hybrid?