Simply because a good design warranties your investment, the design cost is approximately 1% to 5% of the project cost, depends on the application, complexity and project size.

Is common that many projects are still made without a design, using the engineering made by a contracting company, this works often and the system will work, but the decision is made based on price only, this generates system oversized or downsized, also leaving beside other aspects like energy efficiency, air quality, standards compliance, etc.

A good design is the first step to achieve a successful project.