I don't think the main benefit is cutting off cheaters - it is about using the road more effectively. If you have 2 miles of a single lane full of cars next to an empty lane (that is blocked at the constriction), the congestion is more likely to block intersections, ramps, etc. Studies show that having 2 lanes full of cars with a zipper merge at the point constriction is the most efficient:

https://itre.ncsu.edu/itre-studying-how-zipper-merges-reduce-congestion-at-sites-across-north-carolina/