A friend used to say that, he likes to share vocabulary, so they can avoid duplication. Which is entirely true, that said this book gave me nightmare, because I found the mindset so ceremonious; borderline off topic.

Giving name like flyweight to a simple "compression" scheme... The whole thing felt like "duh" to me. Sure it give common ground to people; but none of it felt like something to be written down, even less worshiped like it was.

I also strongly feel about the critics saying that it targets poor OOP languages (cpp, java <5), rendering the whole thing moot in other paradigms.