Taxiing on one engine is quieter and thus more comfortable for the pax.

Also, for ground ops one would want to run HP bleed air since not much air is coming out of the packs with the low power setting. When you use HP in the Saab on the ground, your supposed to have that prop in feather. The Right pack sends most it's air to the cockpit, thus why right side is usually in feather. It's all about the pilots.