It's a significantly more efficient way for dealing with high-traffic in a cross-roads situation (though less safe than traffic signs) and pretty much a must if you get 5 or more roads converging and not enough to space to merge a few of those upstream.
However it takes some practice to be comfortable using them, plus they're most efficient when drivers reliably signal their intention to exit (because it allows people waiting to go in to know earlier that it's safe to do so).