I have one shelf on the left-hand margin of my screen; it is set to auto-hide. Any others (it varies depending on my moods) do not auto-hide.
@Dale okay, so you use an autohiding shelf.
Like Dale I have two production machines without autohide (at the bottom) and one mostly for play and theme work that has an autohide shelf on the left side.
Though see my answer to the stacking question.