All designers have to balance the need for flexibility with the need for usability, because as one increases the other inevitably decreases. Or in c common parlance, “Jack of all trades, master of none”. Systems that are designed to be more flexible have more functions than more specialised designs but are inevitably less functional as a consequence.
The most obvious example of this is the Swiss Army Knife which has added more and more tools over time, increasing its flexibility. However, its inevitable that the corresponding individual tools, such as a pair of scissors, are easier to use than those on the Swiss Army Knife. Similarly, as remote controls add more and more functions, they become more and more difficult to use. Adding flexibility increases the design requirements for a system and therefore means more complexity and compromise.
Flexibility always comes as a cost. Although it is often believed that flexibility is always a good thing, it adds cost, time and complexity and reduces usability. Flexibility is most useful when a system may have a range of uses that are not yet understood or anticipated. Think of the range of applications for a personal computer versus a games console, or mobile phone versus a stand-alone camera. You can use a computer to write a book, keep a spreadsheet of your monthly budget, send emails, save pictures and play games. You can only do the last of these on a games console (and perhaps watch DVDs on some), but the game console does the task much better and is preferred by those whose main goal is to play games.
In trading off flexibility and usability it is important to understand the needs (present and future) of the target audience. The less clear and defend these needs are, the more flexibility should be built into the design of a new product or service. As target audience needs become more clearly defined, usability and specialisation should become more important relative to flexibility. This development from flexibility to specialisation is seen in the way many technologies develop over time and follows the life cycle of products.
In summary, if an audience’s needs are clearly understood then designs should target those as efficiently as possible, whereas if they are less well understood then build greater flexibility and contingency into systems to ensure the widest possible set of applications. Over the lifetime of a product or service, are you gradually increasing usability and decreasing flexibility?
Universal Principles of Design by Lidwell, Holden & Butler