What is the importance of economics in engineering?

Civil engineering focuses on providing basic amenities to the public. Without considering economics, there are very few limits on the scale of what could be undertaken (a 10-bedroom mansion vs. a 1-bedroom cottage). Taking economic restrictions into account, it is the duty of Civil Engineers to balance the opposing forces of cost and product.

Beyond this, as in any industry, if your competetor can provide more for less, assuming comparable quality, they will get the work.