This is the first version of the game that allows the player to reserve land for future expansion, and that has got to be a good thing for those of us who are often confronted with the AI building on land we had earmarked for future expansion yourself.
Jacob has done a great video that show how this works.
On a personal note. You may have noticed that the AI in this version of A-Train is more active than previously. It builds quickly and aggressively. This feature levels that new aggression somewhat. If you want to make the game really hard, don’t use it. If you want to prevent the AI using any materials at all you can reserve the entire influence area of a depot. The more you think about this feature, the more possibilities it opens up.