Did you ever notice when you are building a set that many times the instructions tell you to place a seemingly-useless stud or element somewhere, whose sole purpose is to make sure that kids (or other inattentive builders) don't put another adjacent element in the wrong place, so they wont build the model the wrong way, or have to dismantle a few steps?
I always called them "Don't-Screw-This-Up-Studs" or simply "Smart-Studs". =)
You'll notice them most often when they serve no structural purpose, if they are ultimately totally hidden afterwards, or if they seem like they are just there to prevent common building mistakes, especially where a building mistake would cause a structural misfit, or a weak point, etc.
I think the Pirates of the Caribbean sets have a few... Can you spot them?
What sets have the best examples?