Ergonomic and Human Factors principles, risk assessments and methods are best applied early in the design process and as with most things are most costly to apply retrospectively. They are essential to ensure optimal usability, safety, comfort, efficiency, performance and productivity. Poor design contributes to work-related injurys as well as the root cause of errors and accidents. Human Factors and Ergonomic considerations during design have been proven to pay off further down the line, avoiding retro-fitting and making expensive and time consuming improvements later. Competetive edge and greater user satisfaction also can be given to products, processes or buildings which have been designed considering the end-user right from the initial design concept.

The same principals apply when designing and developing complex systems and production lines. In this case the application is called Human Factors Engineering.

Diagram from excellent source Introduction to Human Factors and Ergonomics