Glass, especially as double-glazed units, is heavy! This means that any opening panels must be properly supported, either at the top, bottom or sides. If supported at the sides, as with traditional pivot-opening doors, stong hinges are attached to the side of the door, requiring double glazed units to have sufficient frame width and strength to prevent the weight of the glass from placing too much strain on the hinges or they may twist or break.
Bi folding doors are made up of a number of doors joined together by hinges, therefore similar rules apply. It follows that frames made of aluminium are stronger than those made of plastic, therefore doors with pvc frames will require more frame per door to provide sufficient strength.
Additionally, though, bi folding doors are folding-sliding doors therefore support is also necessary at the top of bottom of the doors to enable them to slide. As stated, glass is heavy, so doors that rest on the floor will be more difficult to slide than doors supported from above.
The benefit of Frameless Glass Doors is minimal interruption to the views through the windows or doors.
How do Frameless Glass Doors work?
The key is to eliminate the need for hinges. Instead of joined doors folidng as they slide, each door slides and individually pivots open once it reaches the side of the opening - see this 37 second video demonstration:
The doors in the demonstration are double glazed, which is why there is a narrow opaque edge at the sides of the doors - this is the sealed gasket, necessary in kite-marked double glazing, to achieve sufficient thermal values to comply with British building regulations when installed as replacement patio doors.
Interior frameless glass doors for use as retractable room dividers, need not comply with the same regulations and can be supplied as plain tempered glass - single glazed, thick 'unbreakable' glass - with nothing at the sides to interrupt your views.
The Sightline Doors website has images of frameless glass patio doors and frameless glass room divider doors, together with a brief description.