I don’t expect my triathletes to become world class butterflyers and we don’t do enough butterfly to risk injury even if they’re doing it wrong, so I don’t employ many butterfly drills beyond getting the basic dolphin motion down.  I tell athletes to “attempt butterfly for as many strokes as they can until their arms fail to make an above water recovery”.  I tell them to breathe every 2 strokes (or none at all if they can’t breathe without choking on water) and that correct butterfly has two kicks per stroke, but one kick per stroke is fine for now.  The key take away that my triathletes get from Butterfly is it redefines what maximum intensity means to them in the water.  When your body is making symmetrical movements and the stroke requires you to pull back and down as hard as you can to launch your head and shoulders out of the water, a triathlete will contract his or her lats substantially harder than they would when doing freestyle.  I use butterfly as a strength builder and as a tool to get triathletes sprinting freestyle faster.