Need an analogy?
When an architect designs and plans a home, they expect the finished product to exactly match the blueprints they have developed. If they don’t, there is a possibility that the uneven floor resulting from inconsistent construction and follow-through might cause foundational issues down the road.
Why does it matter?
A consistent and uniform front-end is often easier to manage and maintain in the long run. The design team spends time and effort making sure the designs they pass over to the development team are pixel-perfect in how they will appear in the finished product, so to ignore those and cut corners on development wouldn’t be doing your resources justice.
How does it apply?
Digital products are never ‘finished’, meaning they continue to be modified and altered based on customer feedback or new features as the product lifecycle moves forward. A consistent set of design guidelines in place for a continuous product lifecycle prevents the front end code from getting messy.