In Ben Shneiderman's Eight Golden Rules of Interface Design, he wrote: "Consistent sequences of actions should be required in similar situations; identical terminology should be used in prompts, menus, and help screens; and consistent color, layout, capitalization, fonts, and so on should be employed throughout. Exceptions, such as required confirmation of the delete command or no echoing of passwords, should be comprehensible and limited in number."
This is a fundamental principle that transcends throughout the world of design, consistency is a key factor. In Interface design, all of the elements, themes, animations and actions should remain similar through the entire experience. For example, if an interface changes a button color and font during the experience, the user will most likely be confused.
The aspect of consistency also translates outside of one application. For instance, websites tend to feature similar base aspects, company logo on the top left, main menu on the top of the page, and more. These consistencies have developed over time, outlined by usability experts, and adopted into mainstream practice by designers. Therefore, users inherently know how to navigate a website if it adheres to those simple principles. The design patterns we have mentioned before on our blog http://www.ics.com/blog/crossing-domains-patterns-user-experience came out of an overall goal of consistent user interface (UI) conventions.
This applies to all devices and platforms as well. With the rise of multiple platforms and devices, their manufacturers have taken it on to provide guidelines for developers to create experiences that their users can easily understand.
Apple, Google and Microsoft each define guidelines on how to design for their respective platforms, and create a consistent experience for their platforms. Apple mentions consistency in its iOS Human Interface Guidelines: "Consistency lets people transfer their knowledge and skills from one part of an app’s UI to another and from one app to another app." Google's Material Design even talks about how to use animation in a consistent manner.
A consistent interface design is one where the user can learn easily and navigate easily. Overall, consistency in everything we do makes for ease of use, transfer of knowledge and a holistic positive impression. The outcome of true satisfaction from the customer’s experience today will determine the perceived value of your brand in the eyes of the buyer - and ultimately will impact your bottom line business - tomorrow.
1. Eight Golden Rules of Interface Design, Dr. Ben Shneiderman of the University of Maryland, website last accessed January 8, 2016, https://www.cs.umd.edu/users/ben/goldenrules.html
2. Designing the User Interface, textbook, Shneiderman and Paisant, (fourth edition, Addison Wesley, 2005)