Didn't think about that one. Definitely nice for creating Square shaped Tunnels and Rooms because they can be better decorated with WallsYou also can use the stamp tool. It's very useful, if you use it together with the advanced building gizmo.
Is it using push tool or the chisel tool?You can create a Tunnel by using the Terraforming Tool. If you plan to build a Staff Building or something else with a negative Impact Radius, I recommend to build it in a specific Depth because the Radius also goes upwards