Live performance: the musicians face the audience.
Cues are taken from body language and occasional eye contact, but the performance is rehearsed enough that these are minimal.
Reheasal: musicians face each other and take as many cues from each other as they can while learning and arranging the piece.
In addition to facial cues and body language, watching each other's hands can provide musicians with lots of information.
With so many places to look for information, it's hard to recreate a live rehearsal over a distance.
Good audio feedback is a must at any rehearsal. Musicians hear their own instruments in context with others.
Sharing high quality recordings over distance can provide musicians with a good sense of the music, but...
...while juggling so many knobs, cables, keys, strings, and other things, it takes tons of setup time and twiddling before the musicians can actually get down to playing music!
So, any system designed for sharing recordings, video images (of eyes, hands, etc), and voice (to discuss the music in realtime) would have to minimize all this stuff for ease of use.