Key suppliers and key customers are often members of the development team. Once the teams are in place and a detailed project plan has been approved by senior management, the team can speed up its project by doing as many tasks in parallel as possible. Sometimes, it's as simple as releasing work orders for prototype parts as soon as individual component drawings become available, rather than waiting until the entire drawing package is complete. Of course, a willingness to do tasks in parallel means that team members and senior management alike have to get comfortable with the idea of taking more risk. There is little doubt that jumping ahead and doing tasks in parallel is more risky than doing tasks sequentially, one slow step at a time.
Different companies have different appetites for risk.
Development teams need to know how much risk is tolerated in their company. Usually, teams will be allowed to take more risk if senior management knows that the risk is well thought out and understood. Doing tasks in parallel lessens the likelihood that the earlier project work will become obsolete or that the later work will be inconsistent with the work done at the beginning of the project. This minimizes rework or redesign after the project has been completed. Missing a window of opportunity in the marketplace by getting a new product to market too late is a far greater risk than the risk of doing many tasks in parallel.