Working as part of an electrical design team for an expansion to the Alumina Refinery at Gladstone Queensland Australia I experienced first hand the utility of concurrent engineering. We keep forward momentum by guessing missing information and later revising things when new info becomes known.
Using the Project Control Specs issued to all disciplines at the start of the project we electrical designers "guessed" the motor sizes (kW ratings) by extrapolating from similar functions on the existing plant. Using this speculative information we went ahead and prepared our design drawings.
The procurement people got bids from switchboard suppliers and placed orders. As the actual motor sizes were firmed up by the process engineers and this information issued to us we revised our drawings. The procurement people issued the revised drawings to the switchboard suppliers with change-orders and the suppliers modified what they were making. This was an ongoing process until the switchboards were completed.
It was tough on the switchboard suppliers but they coped and it was expensive for the switchboard contracts. But it was cost-effective for the whole project because it saved at least 3 months on the overall construction time. When time is of the essence it pays to guess ahead intelligently and revise later.