A student asked me to expound on foot placement for tango. As someone who has danced tango in parallel for thirteen years, I am working hard to figure out how much turnout works for me and for my students. For those of you who know me, you know that I base my teaching on anatomy and healthy movement for each body.
I feel it is a personal decision whether to turn out or to dance parallel. For some people, only parallel or only turned out movement is comfortable, given old injuries or specific body mechanics. For most people, dancing with natural turnout seems to work best: if you have parallel feet, dance that way; if you really turn out, dance that way. The most important aspect of turnout should be protecting your body. Make sure your knees aren't rolling, that your weight is even on the heel of your shoes (not rolling out or in), that your body is actively stretching and also well-grounded, and that your feet feel comfortable so you can dance all night.
For me, I think my teachers stressed dancing parallel because of my weak ankles: they saw me roll out to the edges of my feet, and instructed me to counteract that tendency. Now that I've been working again with Oscar Mandagaran (and with Georgina Vargas for the first time), I have exercises to do that balance that tendency AND allow for more elegant footwork. I don't have better balance parallel or turned out, but I've noticed some of my students are more balanced now with more turnout. My styling looks a lot better, although I have to focus to stay in the new position, even when just walking--but I can feel when it works well. Because it's easier to see progress on other peoples' bodies, I can really see the difference in my students' movement: WAY more elegant.
Adrienne: hope that answers your questions so far!