As part of the grand backyard landscape plan, we reserved the southwest facing back fence for a line of espaliered apple trees. The idea is to train the trees in a two dimensional plane, parallel to that of the fence, thus taking up little space, enabling considerable fruit production, and hopefully looking great.
I've been an admirer of espalier since I read about it years ago, and have wanted to incorporate the principles into some plants of my own. The espalier propaganda says fruit production is high per square meter of ground space because all parts of the tree and growing fruit are exposed to sun. And disease pressure may be lower because of uniform circulation of fresh air. Most of all, I think espaliered trees are a beautiful and inspiring example of Nature shaped by the hand of Man.