Centric relation (CR) and centric occlusion (CO) should coincide in complete denture patients to ensure stable and balanced occlusal contacts during function. When CR and CO coincide, the dentures distribute masticatory forces evenly, preventing tipping or dislodgement. This alignment enhances efficient mastication by allowing optimal muscle function and minimizing trauma to the underlying tissues. It also reduces the risk of uneven wear or instability, promoting patient comfort and prosthesis longevity.

Reference: Contemporary Prosthodontics, William J. O'Brien, 5th Edition.