What are the drawbacks of forward declaration?

Question

I am wondering if there is any drawback for using forward declarations in all places when possible. This is if my header contains only declarations.

As far as I unde

Answer 1

Forward declaration is the only way to break the cyclic inclusion.

This is the main drawback when not used carefully, I think. I worked in a large project where forward declarations are made whenever possible. Cyclic dependencies were a real problem in the end.