For many situations, the true dividing of the glass is the best way to create a pattern in the window or door. It has been the traditional approach for years and has advantages.
Structurally, the divided lite muntins and bars help to strengthen the sash. They span the stiles and rails and keep parts firmly connected. In steel products this also helps to stabilize the narrow profiles of extra tall or extra wide sash.
When using true divisions each piece of glass is individual for each lite and this reduces the square footage of the glass and therefore allows for thinner glass and ultimately less weight. This plays a role with extra large swing and sliding doors.
In steel products the lock box generally is notched into the glass. The true divided lites can help hide spacer bars and enhance the visual appearance.
Beyond these advantages, the extra material included in a muntin or bar does increase the thermal conduction and the result is a higher U-factor when calculating the unit value.