Why would you print out a hard copy?
The user advocate in me says 'What does it matter why?' (It is simply perverse that saying 'print' does not show me what's on the screen. What else is 'print' for?) But okay ...
The screen interface hasn't been invented (save for such ancient editors as Vi) that allows you to see several distant parts side by side.
You can see a larger chunk on a paper page.
Paper is still easier on the eyes.
Paper doesn't run on batteries, so you're not limited by battery life.
Paper is not fragile and nor worth stealing, so you can carry it to mark up or re-read in places where you wouldn't want to carry a computer. Paper won't be damaged if it's bent.
You can mark up a piece of paper, then throw the mark-up out or disregard it later. Only the most sophisticated version-control systems allow you to do this.
You can mark up things like text rearrangement multiple times without the risk of losing something in the editing, then make the changes in the on-line text carefully and mindfully once you have settled on a version.
I can probably come up with a few more if you need them.