There are countless articles on the internet concerning cloudy windows, but I felt I had to say something, because we see it ALL the time.
The greatest disadvantage in cloudy windows is the hazing between the panes of glass. Some of the time this is only observable in the mornings, after that point it vanishes for whatever remains of the day. Sometimes, it is foggy for the duration of the day.
Insulated windows work by trapping gas or air between two panes of glass that are well sealed. Some windows are loaded with argon gas which gives a higher insulating quality. At the point when the seals break, humid air enters the space. Though it has been shown that as long as there is not rapid exchange of air the insulating properties of the window will remain high.
More times then not, the seal is damaged by the build up of organic materials in the window frame over time. Though, the changes in seasons and the temperature variation between the interior space and exterior space around a home can place pressure on the seals. The jury is still out on long term solutions to the problem besides unit replacement, but a quick search on the internet will give you plenty of opinions.
Came across a quick little article on the internet when doing my own little research: cloudy glass and broken seals