Blurring and / or pixelating

I am curious as to what are the best practices regarding blurring and / or pixelating a portion of a photo. I understand the reasons why the website suggests to put a black box over text one wishes to redact, but for other content that is not text what is the best choice. Should a combination of the two be used or just one? E.g. for blurring a face or something else within an image.

Thanks!