[James_Duval]

There is a huge benefit related to your point about smoothing out human error:

People who pick the wrong lanes can change back immediately and travel the right way rather than either (a) slowing to a crawl with their indicator on hoping to be allowed into the correct lane by some kind soul (who also has to stop/slow down) or (b) looping back round on themselves and trying again.

Obviously, both of the latter solutions add to congestion, and the most common solution I see is an awkward combination of both (a) and (b).

EDIT: In addition, smoother-flowing traffic is desirable in-and-of itself, as fuel economy is greatly improved.