This is a good method. I worked with a crew that put in a lot of posts and they started off doing it the way they were told, but eventually learned to do it this way. So easy.
It was probably not overkill in this situation, but when I took out one of my 4" round fence posts because it broke, I saw that there was no cement around it. But all the posts are fine, except one that leaned over a little. I removed the upper rail and used a come-along to straighten the post, then nailed the upper rail back on. I gues if there had been cement, it wouldn't have tipped and I couldn't have moved it back. One post out of 40 or so is not bad.