Traffic on my commute is generally moving fast enough that it's not necessary. With one exception. There's a stretch of road that crosses over a freeway overpass with onramps/offramps and about 5 traffic lights in the space of a quarter-mile. On my commute home traffic is always backed up along this stretch and I'll split between the two lanes to avoid having to wait through multiple light cycles, rather than riding along the right 'cause there is lots of side traffic in and out of driveways, and cars lining up for right turns. The way I look at it, it'd be ridiculous not to split in that situation.

-Trevor