Cpp Should forward declations be done or not? [closed]

Google's cpp style guide clearly says that forward declarations must be avoided as much as possible. https://google.github.io/styleguide/cppguide.html#Forward_Declarations

But despite the many problems they mentioned, the benefits of forward declaring various definitions are many, and that's the reason we use them a lot in our projects, what are your views? any links to read? what are the suggestions by modern cpp standards coming up?

PS: Please tell me how to put this question instead if you are down-voting.