I think it's mostly that if I take a shot, then tilt the camera down, then bring it back up and take a shot without thinking, the focal length can change on my 24-70mm. I like to fidget and I often knock the zoom or it slides on it's own between shots. So it's a point for me to pay attention to.
Sadly, I also find that I shoot often at one extreme or the other with a zoom lens. I'll either go wide, or full zoom and not use so much of the in between stuff. Which might be why I like having the 16-35 on my camera. It makes me think and use it's zoom in a more considerate way.