This revolutionised the way I look at product development (in my case, software development). It brings together systems thinking, information theory and queueing theory to derive a set of tools to manage product design. The tools are there to influence four design factors: expense, unit cost, product performance and schedule.
Everything is based on an economic model, which is the book's real value. There are no hard and fast rules ("no best practices") because different forms of product development (eg software vs processor design) have different economic properties. Even organisational structure is treated according to the product development model.