LES PORTES VITREES
I have always had some glazed doors in my homes. It just happened that way. My Paris apartments had a few and so does my current house; one leads to my office, another to a media room, to the mudroom from the kitchen and from there to the garage. They do let in a lot of light and additionally are very elegant I find. As our media room occasionally serves as an overflow guest room, and my home office qualifies for some sort of seclusion, those door sport fine linen curtains for privacy. That is the beauty of glass panes on doors: they can all at once be screened with a plain length of fabric and offer separation or invite light and eyes in when and where they are welcome.
Wood and glass
The warmth of wood balances the necessary size of the frames and mullions.
Metal and glass
Doors that open to the outside can be made of metal for security and strength; they are most often finer than their wood counterparts, thus creating a less obstructed view of what lies beyond.
Glass also serves as a very discreet partition where separation but not total isolation is needed.
Closed shutters give glass doors the safety of a wood "shield "against outside elements, the least of which being the heat; open ones let the sun shine in. The best of both worlds.