Why does the lock screen adds a white dot grid over the background image?

Question

I'm already aware of how to remove the dots from the login screen per these questions:

• Unity greeter login screen has a garbled white dot grid?
• How do I remove the dots from the lockscreen in Ubuntu 14.04?
• How do I remove the dots from the login screen?

My question is: Why does Ubuntu do this? Is there a security reason or something else that explains why those dots are added to the login screen?