Can't speak for everyone ofc, but not sure if I ever wanted blurry placeholders when images load fast enough, or found them anything but annoying when not. I think these bells and whistles only serve as designer's self-affirmation.

I've definitely wanted them on photo galleries with large numbers of thumbnails, and I appreciate them when they are implemented well, especially if I'm on a slow connection.

Agreed, they just create needless visual activity. How about a page specify where the images appear, and leave it up to the browser to decide how to show them and load them? Is that too simple and workable?