Like if you want to copy a long thread, with lots of images, you click ctrl + a and then ctrl + c and it only copies the text, not the images because when you click edit now it shows the images instead of the image links.
This is the old way it would show if I clicked edit:
Top right of the reply box has a button that has A's in it. Hover over it and it'll say 'switch editor mode'. Click it to change the code of the text (ie from copying images to the [img]www.example.com/image.jpg[/etc] format).
You can also change it from the control panel in options I believe.