Why are shop drawings so important?

Shop drawings are part of the larger Construction Document Submittal Process, which is required on all significant construction and restoration projects. Submittals are required primarily for the architect and engineer to verify that the correct products, methods and services are being utilized on a project. Submittals are based on requirements documented in the Construction Specifications. Submittals are not an opportunity for an architect or engineer to change their specification requirements, but rather to confirm that their specified products, materials, services, colors, finishes, etc are complied with from the various suppliers and subcontractors on a job. Upon approval of the shop drawing in the submittal process, the shop drawing becomes part of the contract record and the basis for what the architect and engineer will accept upon delivery and installation on the job. For an excellent reference on the subject, see the Robson Forensic article The Importance of the Construction Submittal Process.