Usage of protobuf classes after deserialization

I am using protobuf C++ and I read that protobuf is mainly supposed to be used for serialisation and deserialization between endpoints.
I was wondering if it makes more sense, performance wise, to actually have pure c++ classes that I map the protobuf classes to after deserialization, use them for the program logic and then convert them back to a new protobuf object before sending them back?
I imagine mainly copying protobuf objects is quite costly.