@goldfinger, care to illustrate an example?
I know that you can attack your own unit to defend the position, but when do you support an enemy into a position that you hold?
Say, for example, we had German: A Mun, A Hol, A Kiel
and French: A Bel, A Ruhr, A Bur.
So, Ruhr can be defended by A Bel S A Bur - Ruhr; (by two, supporting Ruhr to hold can get it three)
But instead, I could order A Bel S A Mun - Ruhr (and this will be cut if and only if it would make Ruhr dislodge) If however Germany orders A mun - Ruhr, A hol S A kiel - Ruhr (for whatever reason) Then belguims support will cause a bounce between munich and kiel. (not dislodging the unit in ruhr so the support isn't cut.)