While I think it's beneficial for a follower to know where the leader's feet are, that's only because it lets her be aware of what the couple is doing as a whole and have a greater appreciation for the dance she's half responsible for producing. What you are talking about is... well, let's just say it's not the way people lead and follow in tango! The lead for this movement (i.e. the follower sticking her free leg out) is a tiny impulse in the direction the leader wants her to place her foot, without him taking a step and doing a weight transfer. As soon as he's sent this impulse, he can then move his own free leg/foot however he chooses (in the same direction or any other). If executed properly, this creates the illusion of simultaneity. This is the same fundamental technique used in walking, just broken down into its constituent parts. Everything is felt through your partner's body. As a leader, I feel my partner's feet through her body, just as she feels the lead through mine. Good dancing has nothing at all to do with sight and little to do with pushing: it's about signal transduction, plain and simple. For instance: he creates a larger impulse so that she places her foot farther (sinking down slightly makes this message even clearer). Then he takes a shorter step than the one he led her to take. That's one way... there are many others.