Actually the optimum way to move the most cars is use all of the space - all the way to when the lane ends.
However, cutting into the empty lane from another lane just to move ahead afew cars is indeed an ******* thing to do. Even more ******* than this though is intentionally blocking people that are in the ending lane from merging, if you do this you are the one creating extra traffic, since again the ideal way to move the most cars the quickest is to use the lane until it ends.
This is a common misconception that people can't seem to let go of, that you need to 'merge as soon as possible', this is not true. This and also the idea that if other lanes slow down you are entitled to have your lane continue moving at normal speed while people in lanes near the slowed down lane sit still with blinkers on trying to escape the jam.
This page does a good job of explaining:
http://lifehacker.com/the-right-way-to-merge-lanes-to-avoid-traffic-jams-and-1501148503