I know that from the mathematical point of view it doesn't matter if we plot Bode diagram of stable or unstable system. It's just a function of complex value.
However from the physical point of view, Bode plot shows steady response to a sinusoidal input. If the system is unstable there is no steady response, am I right? So is it only a "magic" of mathematics that although there is no meaning, it's still useful to use it for design?