There are many advantages to doing window glazing and we are going to name a few. Starting with energy savings. A lot of times when windows are old, they get openings were the glass and the wood frame connects, letting air escape through this cracks. In the winter time hot air escapes and in the summer time the heat comes in through this cracks. A window glazing job will greatly reduce the amount of air leaking and less air leaking means lower heating/ac bills.
The second advantage besides saving money on heating and AC is that the cost of replacing a windows is usually 3 times what it would cost to glaze them if not more. When glazing a window, there is also the full restoration process involved. Caulk on cracks and gaps, wood filler on holes, scrapping, priming and painting.
The other advantage of window glazing is that you keep a window that is Vintage looking which gives a beautiful sort of classical look to the exterior of a house.