Oh, here's a fun example. Go look at the 'Elemental Catastrophia Info Dump' thread, particularly the entry for dark ragnarok/ultimate (the lv 70 one).
Imagine you're using some soul with a buff that targets other players too (mainly Arthur's atk buff and the defense buffs from Cassiopeia/Andromeda, right?). Let's say you use that buff on turn 1 and happen to also tag some other people with that buff before they get turn 1 out of the way..... :P