Often, designers add a feature because they do not know customers' preferences. Often, they add an option because they are not sure how the users prefer to use the system. Often, they believe that the system should work in one way but add the option "just in case.”
The modified version of the principle of parsimony uses terms of cost effectiveness. Adding a feature usually causes usability difficulties. Adding an option to improve one aspect of usability often reduces other aspects of usability.
The modified principle of parsimony states that we need to have very good reasons why we should add a feature or an option. "Just in case” is not a good reason. Flexibility or other slogans, when accompanied by hand waving, are not good reasons either. Good reasons should be related to main user tasks and should be justified through task analysis.
A feature or an option not required for a main user task should be eliminated from the interface design.
Updated on 28 Feb 2016.