Before Ambitions, you could not place down
any new empty lots. Ambitions added the World Editor tool, which enabled you to add new vacant lots. I haven't added any new lots to my town yet, but there are many different sized lots you can place and you do not have to put them down connecting to a road (like in TS2). The new lot sizes you can place are 10x10, 15x10, 20x20, 25x20, 25x25, 30x20, 30x30, 35x25, 40x20, 40x40, 50x25, 50x50, 64x64. You can also place or change decorations to your town, didn't write down what the other tabs were, but from what I remember you can add trees, rocks and misc. You cannot add roads with the WE (World Editor).