You should add missing foreign keys to ensure data integrity and generate accurate database diagrams. However, don’t add all of them at once — do it in phases. First, check for invalid data that may violate the constraints. Adding too many FKs at once can cause locks, performance hits, or app errors if the data isn’t clean. Test changes in a dev environment, fix any orphaned rows, and roll out gradually. This improves design, avoids bad data, and helps tools like SSMS show correct relationships.