I do think it's a good feature, but obviously, it seems pointless in that point of view, making a hidden photo.
But, in some occasions, I missed that feature and how helpful it could be.
You know when you show some photo to someone and they automatically start pushing photos left and right without permission, acting like a green light to see all your photos? That's when I hoped to have a feature that allows us to hide some photos from the camera roll without being to obvious.