One major rationale behind "effective separation" is the need for maximum flexibility in the code and resources dedicated to the presentation logic.^[2] Client demands, changing customer preferences and desire to present a "fresh face" for pre-existing content often result in the need to dramatically modify the public appearance of web content while disrupting the underlying infrastructure as little as possible.

The distinction between "presentation" (front end) and "business logic" (infrastructure) is usually an important one, because: