My choice: CH 13: the STOP Block

This Block is like an emergency stop button.

"If your robot encounters a STOP block at any point in the program, the robot will simply stop at the point with no further action."

Usually, the robot will stop, when it completes the all the actions, which are programmed.

However, this STOP block will immediately stops the robot, no matter what action it was doing, or have not completed all the programmed actions.

Only the exception is when you are using a data wire and is providing a false input. (I need to go further to explain about this. Will learn later.)

This block will be useful, when I want my robot to just stop and do not do any action.
Also, if I want my robot to stop from going forward, I usually put 2 move blocks, which says stop. But, putting one STOP block, I can stop my robot from going forward, and it saves space and effort.