The computer display is visual, it cannot produce other sensations like touch and smell. The experience of using an abstract digital interface is thus limited to the visual. By using skeuomorphs, designers aim to elevate the experience to a higher level by means of association.
In other words: we know what a physical material like wood smells and feels like, and those sensations play a part in our relationship with it. We enjoy the texture, the feel of it, the smell, which is why its textures are oftentimes imitated on cheaper firniture and fooring. In the same way, the skeuomorphic interface that uses wood textures on a computer display aims to capitalize on our favorable disposition towards this material by getting us to recall those positive associations. It cannot reproduce the sense of touch or smell, but it doesn’t have to because those things have already been experienced by us before. All it has to do is imitate the texture convincingly enough and it will succeed in evoking a positive emotion.
In a way, the skeuomorph is a reaction to the severe constraints that the computer display imposes on the experiences that the designer wishes to create. It’s a way to break out from those constraints–if only a little–and extend the experience to a level built on the other senses.