Allows you to place entities that automatically get removed one minute after you last placed a temporary blocking entity. (The 1 minute duration is configurable in the mod settings.) Who said you couldn't have a straight wall and a corner wall in the same blueprint?
If you don't want the AI placeholder art anymore, feel free to DM me with your suggestion for how the temporary blocking entity should look.
*In order for these train blueprints to work in Factorio 2.0 you need to remove stock_connections from the blueprint: https://forums.factorio.com/viewtopic.php?t=124373