Laying out a complex, site, plant, or unit can be a challenging exercise. There are safety, environmental, financial, and public concern risks to balance with project cost and schedule goals. There is a large amount of both site and process data to be gathered and considered in the layout and spacing process. This is a cost effective way to manage risk. This minimizes the probability of an incident occurring or escalating because higher risk equipment is located away from lower risk equipment. It also allows risk minimization measures (e.g., fixed protection systems, containment systems, detection systems) to be installed efficiently around the higher risk equipment rather than across the entire site.
Reference: CCPS: Guidelines for Facility Sitting and Layout