First off, I would like to say consistency is an important factor in web design. Color, fonts, layout and nomenclature should remain relatively consistent throughout the user experience. However, it should not trump all other considerations. For example, I was recently working on a registration process in which the user had the ability to print out a contract before making a final decision. The main objective was to assure the user that the company was being transparent and could be trusted. In an effort to emphasize this to the user, I had placed the print button in very close proximity to the actual agreement on the page. This way the user would immediately recognize that they had the ability to print the agreement and review before proceeding forward. The client's immediate reaction was to comment that it wasn't consistent with the placement of print button on other pages. For them, the print button should always remain in the upper left-hand corner of every page. For me, this defeated the purpose of providing the print functionality or displaying the agreement all together. By placing it far away from the agreement, it would more than likely be missed and only add visual noise. The whole objective of being transparency and trust was lost.
This is where the concept of consistency breaks down. Consistency doesn't take context into consideration. To remain consistent at all costs sometimes blinds the user to useful information that could have moved them to complete a task or make a decision. User experience design is about knowing when to be consistent and when to break the rules and provide the user with the right information at the right time.