Cnn_regression y_range

I dont get why we want to force the model to output activations in the range (lo,hi). this is in lesson 6 at 1:18:49
Why is it that in the video there is a small part that says coordinates are always rescaed from +1 to -1 but this isnt the case in here ?

Rather confusing Mr Jeremy hasnt really told us why we rescale it or rather. I havent picked up in that