CJ Nielsen discusses the importance of proper planning for mechanical space layout in a building project to ensure functionality and aesthetics. He showcases an example where all mechanical components are strategically placed out of sight, making the space more efficient and organized. Planning ahead for equipment expansion and future additions is crucial, and coordinating with architects and builders early on can lead to a well-designed and versatile mechanical space. Nielsen highlights the benefits of having a designated mechanical room for storage and maintenance, emphasizing the significance of considering space allocation and functionality in the overall building design process.