This is a wonderful topic, with so many ramifications. More, please!
Bart, I'm curious about your remark concerning watching DVDs with the sound off. Why can that be glorious?
Patrick has already said most of it for me. I'd add an important ingredient: the dancers in these dvds, as opposed to those created without music, WERE hearing the music as they danced. They are supported by the music and can respond to it. Their performances are truly "musical." What we see is a kind of distillation of what mkusic has helped them to do, but in movement terms only.
Barbara's story about Paul Taylor's dancers is a propos. These dancers learned and rehearsed the parts to music. The music remained in their heads. They were, in a sense, still
dancing to the music, even though the audience could not hear it.
This is in no way a substitute for the full productionl As Patrick says, watching dance -- especially Balanchine, for me at least -- is "a good exercise in several ways." Nowadays I typically watch an MCB program 3 or 4 times in a single weekend. Most often the program is composed of works I have not seen for a long time, frequently for decades. Watching a video twice -- once with the music, once without -- is very helpful in bringing back my visual memory. The second viewing -- the one without the music; the one that demands most of the eye -- is the one that most often makes me realize just how miraculous the human body's flow of movement through space and time can be.