Absolutely.
If you only insulate the façade and keep the old windows, the weakest point in the house remains uninsulated (the loss of heat from a house through the windows is up to 30%!), there is a much lower energy saving effect and heat continues to be lost through the façade.
If you replace only the windows the condensation – which would otherwise form on the poorly insulated window – is deposited on the cool wall. This can result in the formation of mould harmful to health if there is insufficient ventilation.