There are several benefits to new windows, principally that they will better insulate a home, keeping out drafts and keeping in heat, so energy bills may be reduced. Double paned windows will also keep out street noise. This can be a major benefit in a city with lots of traffic or noisy tourists like Paris, but noise reduction hardly seems necessary in a peaceful village like Lonlay l'Abbaye.
In any event, Joseph and I like to look out at street life wherever we find ourselves. Hearing a town or city waking up around you motivates you to pour that coffee and get going. When you see people bustling about, you can tell how cold it is outside, whether or not you need a jacket, whether or not it seems to be a holiday of some sort, and what kind of deliveries are being made fresh to the nearby shops. And there is the endless charm of seeing and hearing parents and children together, funny dogs with their owners, or couples in love, both young and old.
This sense of joy and connection to others who are joined with you in the daily life of a town, this gentle chaos of variety, is what Impressionists like Renoir and Pisarro captured so well in 19th century Paris:
Romanticizing old style windows is one thing, you might say. Do you want to have drafts and spend extra money wasting heat? Well, no. The fact is, however, that only about 15% of heat loss is through windows. Less if they are fairly well caulked and fitted. Much more is lost through a non-insulated roof or floor, and I'm sure our builders will remedy that.
Many new windows are made of PVC plastic. They may be energy efficient in holding in heat, but they are not "green." Preserving existing windows is more environmentally friendly, especially when you consider that most PVC windows will have to be replaced every 25 years or so. Unlike the old wooden windows, they cannot be repaired.
Yes, new windows will function perfectly and can be airtight. But do old buildings really want to be airtight? From what I have read, the answer is no. They were designed to pull in fresh air from outside, circulate it and feed the fire burning for cooking and warmth. So if there are some little drafts around the closures, that's ok with me.