Are unused includes harmful in C/C++?

Question

What are the negative consequences of unused includes?

I\'m aware they result in increased binary size (or do they?), anything else?

Answer 1

Yes, they can increase binary size because of extern unused variables.

//---- in unused includes ----
extern int /* or a big class */ unused_var;

//---- in third party library ----
int unused_var = 13;