I watch a lot of videos on Youtube (at the time of this posting over 7500 mostly tango related). I know, I should get a life, but remember, I live in a Tango Wasteland. As it turns out this may actually stimulate the same areas of the brain that are used during the actual dance (see the link below for reference if you like).
I am not saying that one can learn to dance Tango on the internet, they cannot.
I know one couple that took a few lessons and decided they could study this way and improve their dance. They do dance, and it is unique. It is not tango by any stretch of the imagination, mostly a lot of very poorly executed big moves (volcadas, leg wraps, ganchos, etc... mixed up with a few snipets from other dances all smashed together) Painful to watch! Painful to be anywhere near them while they are dancing, yet they enjoy themselves (who am I to judge).
On the other hand according to this article once someone has a personal knowledge of a dance and has experience actually dancing the dance they can process what they are seeing and actually learn something purely through the visual.
There really is no substitute for one on one personal instruction from a competent instructor.
ref link
Also this
