Because he used the term "blitting", which means moving a block of memory. I assumed he wouldn't use the term unless he knew what he was doing and what he wanted, otherwise he'd just call it drawing part of the image or something.
As for why he would do it, I don't know exactly, but there are examples. Like a Worms-like game, where you want destructable landscape.
As for why he would do it, I don't know exactly, but there are examples. Like a Worms-like game, where you want destructable landscape.