This feature allows you to edit multiple lines in one go. Why? ever wanted to change the access on multiple class members (eg: private to public).
Basically you hold down the ALT key and drag a selection rectangle in front of the lines where you want the edits to appear and then start typing. Though this is hard, especially when you are working on your laptop.
So instead, use the shortcut key ALT+SHIFT+(down or up arrow key) to create the selection rectangle (in the red circle) and then start typing