Regardless of style--apilado, milonguero, salon, nuevo, whatever--I use my whole foot pretty much all the time. I try never to dance on my toes. (I'm also lazy, and averse to pain...and dancing on my toes is both tiring and makes my feet hurt much sooner. Besides that whole "being bad technique" thing.)
On the toes, never. Ouch, poor toes!
On the ball of the foot, yes.
Whether or not the heels ever rest on the floor depends on a particular dance, partner, music, at times, on the shoes (heel height) I am wearing. Whatever works best.
The weight is kept pretty much forward in any case.
Watching all the videos of young dancers in tango, one might conclude that a woman should dance with her heel tips lifted. Ask yourself, how many ballroom dances require this? The answer is the same for tango. Raising the stilleto heel tip off the floor is the current fashion in tango among trained dancers, but that doesn't mean it is correct.