Courtyard walls and garden fences are great for giving you shelter and privacy, but unless you're a Tall Black, they're likely to obscure the view of your garden. Unless you have a window, that is.
Obviously, it's easiest to incorporate a garden window when you're at the construction stage, although the disadvantage of that could be that you won't know how your garden is going to develop.
But even if you already have garden walls or fences in place, it need not be a major to put in a window.
In our early days of DIYing, we didn't quite have the confidence to knock a window space in our concrete block courtyard wall so, instead, we cut out a section of blockwork at the top of the wall, then added a timber capping across the gap. It looks quirky and original, and gives us a view of the foliage on the other side. More recently I've considered making a head-size hole low in the wall so the dog can see who's coming down the driveway without jumping over, but that's still on the drawing board.
Bear in mind that if the point of adding a window is to open up a view, then make sure you can see whatever it is without having to move your chair or crane your neck.
Your window should frame a vista, a specimen tree or a garden bed and, once it's in place, you can plant outside of it to enhance the view, or change it according to the seasons.
The other great reason for adding a window to a wall is because the wall is pig ugly. Long, unrelieved sections of corrugated iron or panel fencing are often seriously unattractive, so the addition of a window can add interest and even a sense of mystery. If such a window looks out on the next door neighbour's collection of dead cars, use a mirror, instead. It'll open up the space on your side and you can position beautiful plants, pieces of garden art or yourself in front of it.