You may sometimes blur out images of your private information such as bank account number or social security in order to share pictures. But now even that can be hacked.
For the most part this is all fine with peoples' faces as there isn't a convenient way to reverse the blur back into a photo so detailed that you can recognise the photo. So that's good if that is what you intended. However, many people also resort to blurring sensitive numbers and text. And this is a bad idea