If you have a lot of cars coming up to a "merge point" should you merge at the point when the lane actually ends, or 5 miles before that? By merging earlier you are just moving the merge point back and slowing traffic earlier than if you merge at the point where the lane ends.
We should use the maximum amount of lane space and merge as late as possible. If everyone did this the backup would move up farther (closer to the merge point) and not affect traffic as far back.