Material saving: compare with 60mm window frame and sash, 50mm window frame and sash saving 20% PVC profiles and steel reinforcement.
More light: For small window, if use big profiles, less glass space and get less light, 50mm with small section, makes room more bright.
Easy to install: Less weight easy to move and installation.
Easy to open and close, more easy than 60mm series.
Saving, but not loss any function.