Things may change. Read this:
http://www.straitstimes.com/news/sin...illes-20150125
Actually an owner could always leave one panel open or some other means to fit the description. A comparison is with those bamboo or roller blinds. When they are lowered the balcony is fully enclosed and covered too just like the glass curtains. When they retract, so can the glass curtains to reveal the full balcony. In terms of facade that glass curtain introduced less change.
I visited the show room for Jade residences with movable panels that can span the whole balcony. Yes, the panels are interleaved and have gals horizontally. But an owner can easily install glass panels behind and I doubt anyone can tell the difference from the outside.
Anyway, my balcony is not of a size to benefit. 4 bedders and maybe 3 may have practical use.