The database design task is a much longer activity and the database may be poorly structured. Since not all business data requirements have been thoroughly flushed out, database designs are unstable throughout the development process. Resulting databases may be poorly structured, looking like a patchwork quilt, instead of being well planned and easy to maintain. Errors in the database design will cause the entire system to be unusable. System documentation doesn't get created, or is textual vs. graphical and difficult to maintain.
User requirements are lengthy, textual documents that are time consuming to review.
Without a logical model to refer to, data definition language must be referenced when planning system enhancements. DBMS systems often limit the length of column names making them difficult to decipher. An ERD is a structured, graphical document that describes the business supported by the system. Logical data modeling forces analysts to think about the current business requirements, independent of technology, thereby highlighting opportunities for business process improvement rather than simply automating an existing procedure or recreating a legacy system on a new platform. Users' understanding of their current systems can prevent them from identifying the true business requirements.