A recent poll on Lifehacker asked if an intuitive user interface was more important than functionality. The default answer is that content is king – therefore functionality wins. An intuitive user interface that does nothing useful serves little purpose. However the question is too short-sighted because it does not examine the relationship between intuitive and functional.
Firstly the question implies that there is a tradeoff between functionality and intuitive. This is not true because an interface can be both intuitive and functional at the same time. The two attributes are only rarely mutually exclusive. Good knowledge of the target audience (users) enables a designer to create user interfaces that are intuitively tuned to that audience in ways that provide the most functionality in the simplest possible way.
Consider productivity which is calculated as outputs divided by inputs. An interface’s outputs are the functionality it enables. The inputs are the costs of achieving those outputs which in interface terms is crudely the human time taken to achieve the outputs. This means that an intuitive user interface has higher productivity because outputs can be achieved in less time than with a less intuitive interface.
User Experience designers also consider the connotative side of productivity. They consider the feelings that the experience of using the interface will produce. These emotions are an important part of the overall message of the interface and should be support the brand message of the user interface’s creator. Feelings such as a sense of control, delight, ease, efficiency are all things that an interface can engender. Interaction is therefore must be considered strongly for its semiotic content alongside the traditional static visual communication based on composition that designers are used to. In static compositions perhaps color carries the most connotative meaning, but in a user interface interaction can surpass color in terms of the amount of meaning carried.
Accuracy is an important part of productivity. Even trained users make fewer mistakes when using an intuitive interface. Each mistake reduces productivity because it either takes time to fix when noticed or creates a negative output when not noticed.
Technological progress goes hand in hand with productivity. Functionality alone is not a good measure of progress because while functionality dictates what technology makes possible, productivity dictates what technology makes pragmatically probable. For example much of what jQuery does today for web designers has been functionally possible for over a decade however it took toolkits like jQuery to simplify things so that the time (and skill level) required to produce those outputs was reduced enough to tip the productivity equation in favor of more interaction on web pages. Also, computers have become cheap enough, fast enough and capable enough that they have almost completely surpassed traditional forms of doing graphic design in terms of productivity.
There are many more examples where convenience (reduced input) of technology has tipped the productivity equation in favor of greater adoption of that technology. As we expand our use of technology we see gain the view from a new creative horizon so therefore can look for even more ways to improve productivity.
If a user interface is just too difficult to use then the productivity equation swings away from convenient usage of the interface because the outputs are not worth the inputs. Therefore a user interface that has high productivity i.e. both functional and intuitive is more likely to achieve greater usage.