Why are sash windows best for aesthetics
The human eye has the ability to read lines and angles extremely well, to see if something is balanced or unbalanced. Palladio understood this more than most.
He drew an arc from the width of a window, which equalised the shape of a window and meant that the glazing bars were equalised and the finished design, well balanced. Sadly, many modern window designers have lost this principle, most window producers or installing companies provide unsympathetic products, which have totally destroyed any semblance of his theory.
Most box sash windows were traditionally fitted behind the outside brick or stone so that the bulk of the frame material was hidden from view. This design became law following the Great Fire of London to prevent the spread of flames whilst allowing maximum daylight into the rooms.