More from less...
Maximise small window openings
A French window allows for more practical use of smaller window openings. In first floor applications for instance, the ability to gain unhindered egress from a window that fully opens without the frame having a fixed mullion has immediate fire escape use. The added bonuses being greater ventilation irrespective of wind direction with rapid venting on those hot days and nights!
The paired opening sashes naturally create an equal sightline appearance.