I was reading some C++ object-oriented programming notes that mentioned that we should avoid wrapping functions in classes if it is not required, since wrapping 'things' in classes reduces efficiency. Is this true? If it is true, then what exactly does/could it mean when it says 'things' (this seems to imply that this efficiency reduction is not limited to only when wrapping functions in classes)?

I was reading some C++ object-oriented programming notes that mentioned that we should avoid wrapping functions in classes if it is not required, since wrapping 'things' in classes would reduce efficiency. 

Is it true that wrapping functions in classes reduces efficiency? What other 'things' could reduce efficiency when wrapped in classes?

I was reading some object-oriented programming notes that mentioned that we should avoid wrapping functions in classes if it is not required, since wrapping 'things' in classes reduces efficiency. Is this true? And what exactly does it mean when it says 'things' (this seems to imply that this efficiency reduction is not limited to only when wrapping functions in classes)?

I was reading some C++ object-oriented programming notes that mentioned that we should avoid wrapping functions in classes if it is not required, since wrapping 'things' in classes reduces efficiency. Is this true? If it is true, then what exactly does/could it mean when it says 'things' (this seems to imply that this efficiency reduction is not limited to only when wrapping functions in classes)?