The book looks at what it means to say something has 'quality'.
It didn't teach me any new philosophical methods or theories, but it did make me look at my own work differently and start asking: how can I make something with the highest quality? What compromises that quality? What is a method that leads to the highest quality?
Translating that to my business life: in the startup scene I've scene a lot of startups treat lean as gospel (myself included at one point), and as a result they compromise on the quality that both themselves and their customers are happy with. So I certainly found it useful to have a book that made me think about this.