BIM Modeling based on existing 2D drawing can be beneficial for Client for a lot of reasons:

• existing 2D design is developed but there is uncertainty in its quality and consistency;
• brownfield projects is the case so you need to fit new design into existing building or facilities;
• for operation and maintenance purposes where as-built BIM model become reliable source for rapid data access; etc.

Design in 2D is limited due to its nature, as it is represented by lines, polylines and generic geometrical shapes with constant need to keep it in order and up-to-date. The collapse starts when we need to coordinate disciplines or make some major change. The task to deliver consistent design becomes practically impossible, as can be observed especially on complex industrial projects (this case).
BIM design instead is represented by graphical objects with their own functional characteristics and properties, linked and enhanced with specific information needed for further use. 2D drawing and specifications are just derivatives extracted out of BIM model. The benefits are:

• design using BIM is faster, can be thoroughly explored, coordinated and improved;
• clashes between disciplines are identified at early stage, significantly reducing or even eliminating on-site clashes;
• more effective communication, visual review possibilities;
• ensuring prefabricated components fit correctly into designed spaces, etc.